Of course it would not sound like that in the middle of the nave. The microphone does not pick up the confusion of noise down there! I can barely hear the choir organ at the beginning, supporting the congregational singing (and the celebrant) [This Mass would, if normal, have just a cantor and the choir organ]
"out the door so fast" the building is too big for that, but the traditional joke holds at Westminster as well "What do you call a musician who's audience gets up and walks out while they are playing? ... "
I see there was an organ recital scheduled for before that Mass.

Hmmm. I'm not a fan of that particular improvisation. Seems excessively concerned with theatrical dissonance. One can play a "wild" and exciting improvisation without sounding, for lack of a better word, ridiculous.

I am a definite proponent of the French school of organ improvisation, which while sometimes employing strong dissonance, is so clearly based on Gregorian Chant that it definitely combines the brilliance of the great organists with the beautiful patrimony of Catholic music. I strive in my own limited abilities and ways to improvise in a similar fashion to the French School. But the improv linked by the OP is just way out there, not pleasing to my ear at all, seems to have no discernible structure, doesn't really develop and build... it's just a bunch of notes, and they all sound wrong. Irishtenor may be right: maybe if it was transcribed, we could find some stroke of brilliance in it. Or maybe my ear and music theory knowledge are inadequate? But as someone who loves grand organ improvs, and who enjoys Messiaen et. al., this particular improvisation was not at all pleasant to my ear, and I'd personally consider it to have crossed the line, as it were, into the realm of "not really appropriate for the liturgy." The dry acoustic from a close recording doesn't help, to be sure. But even in a nice 4 second reverb, I don't think that would sound decent. But what do I know? He's the Master of Music at Westminster Cathedral, and he's won awards for his improvisation, so I suspect he knows a bit more than I do. But that doesn't change my opinion on the matter!

Here are some recordings that I think exemplify good "wild" improvisation, all fitting for the Easter season:

https://www.youtube.com/watch?v=Ye9zYe3ci48
https://youtu.be/2EBCAk2IFwU?t=1m38s
https://www.youtube.com/watch?v=FbK-7QPjRVI
https://www.youtube.com/watch?v=gB53YDLS8Aw

Now for non-liturgical improvisations, I have to say that this remains my all-time favorite: https://www.youtube.com/watch?v=jM5wp82ghuw

If it helps, here is an example of what I'll do in an improv in a parish church setting. It's nothing like the greats of improv (imo: Daniel Roth, Olivier Latry, Cochereau, Tournemire, et. al.)... this was just practice, playing around with ideas, so forgive the couple of obvious moments of uncertainty. But at least it's a real and practical example of a pseudo French school improv, played in a parish church setting. I played an improv based on some of these ideas on Easter Sunday as an interlude between the Last Gospel and Exposition/Benediction (which we do every first Sunday). It was well-received. But they're accustomed to my improvisations by this point, I suspect.

https://www.youtube.com/watch?v=b2C6qD5ObyQ

This can hardly be called 'improvisation'. There is no music. To echo Francis, there is no content, no musical form or didactic. It is pure noise-making devoid of any motivic, colouristic, or formal interest. I've heard similar from others, including some of the prominent French, Latry, for instance. The unfortunate thing about the organ is that, for many, all one has to do is make a lot of noise and the astonishingly unwitting and undiscerning masses are impressed greatly. (Indeed, did you notice the applause after this inane exercise was ended?) No wonder real music, say a trio sonata, goes right over their heads. Theirs is a circus music mentality, and the 'musicians' who cater to them are not worthy to be called musicians of any kind, let alone organists. The hands and fingers aren't even musical to watch, their movements are animalistic, tight, clenched, and grasping, all without purpose. An utter bankruptcy of musical thought.

@M. Jackson Osborn

I've heard similar from others, including some of the prominent French, Latry, for instance. The unfortunate thing about the organ is that, for many, all one has to do is make a lot of noise and the astonishingly unwitting and undiscerning masses are impressed greatly. (Indeed, did you notice the applause after this inane exercise was ended?). No wonder real music, say a trio sonata, goes right over their heads. Theirs is a circus music mentality, and the 'musicians' who cater to them are not worthy to be called musicians of any kind, let alone organists.

I certainly agree with your assessment of the improvisation in question. It may not even be fit for the circus.

But with due deference to the legitimacy of varied aesthetic preference, I think it unfair and inaccurate to paint with so broad a brush the French school organists like Latry. And forgive me if I've misunderstood what you're saying.

It's a different school of thought, yes. But circus music? I don't think so. The French school remained more faithful to Catholic music over the years than any other school, in my opinion. The French school of improvisation has built on the legacy of the great French Romantic and subsequent composers (like Franck, Widor, Vierne, Tournemire, et. al.), tailored, of course, to the wondrous resources of the Romantic organs like Cavaille-Coll's instruments. Gregorian Chant is its primary melodic inspiration. If you listen to the really talented improvisers of the French school, there's no lack of content and musical form. The French school may not employ the same consistent logic of counterpoint and strict forms like fugues or trio sonatas. But in my opinion, that is precisely its strength. It is more free to paint with a much broader palette. That's also its weakness, since it can obviously get out of hand. But applied well, the French improvisation style can be remarkably effective at expressing sacred ideas through music, and lifting the heart and mind to contemplation of the various splendors of God.

Consider this improvisation by Daniel Roth: https://www.youtube.com/watch?v=bxJuwWP_s6Y

Or this by Latry: https://www.youtube.com/watch?v=dxMkmOEkcBA - This one's a bit more "French" than the Roth improv above, but I find it quite prayerful, and a fascinating development on a simple theme. But for something more traditional, here: https://www.youtube.com/watch?v=qTAh56P7Wd4

With all of that said, let me back up a moment. I do agree entirely that noisemaking is nonsense, and all too many organists conflate improvisation with loud noisemaking. That's unfortunate. And the OP's link... that's definitely nothing more than noise in my opinion, and I'd be fine with labeling it circus music. A big acoustic and a full organ and a lot of notes can get applause, but it's not music on account of those characteristics. However, I don't think the way that Latry, Roth, et. al. improvise is like that at all.

Well, at least the subject of the improvisation is clear enough ("Deo gratias, alleluia...").

Yaknow...liked it much better second time round.

Here is another of his at a distance recording. https://youtu.be/o9WhBwKJKCw

It's not my favorite specimen of the improvisation genre, sure, although I can attribute some of that to the crummy speakers on my phone. But "trash"? Trash, folks, is the National Enquirer, the paintings (and the biopic) of Thomas Kinkade, and the novels of Danielle Steele. The only offensive sound I heard was the applause at the end.

This is coming from an "uncultured" non-organist, but do I really have to listen to this? Use this for your organist competitions. Not after divine worship.

If we want to critique the OCP sacro-pop, all fine and well, but we have to be fair and let the sword cut both ways.

Gracious!
I couldn't do that.
Just think what he could do with Puer natus est!
Or Jubilate Deo.
Or Confirma hoc.
Or Terra tremuit!!!

Bovet played a recital at one of my churches once upon a time.
He has a well-earned reputation for having a highly idiosyncratic approach to improvisation.

A very congenial fellow. At drinks afterward he described a friend of his who happened to have buck teeth as having 'teeth en chamade'.

(Is this wild enough?))

Heh! Not particularly wild, but that was a fun start to my Saturday.

I could do the entire 1940 this way, and it would STILL rival anything out of OCP.

gotta love garageband...

I'm tempted to ask in which category this would rival OCP.

musical, artistic, true beauty (not liturgical, which OCP is already NOT)

OK... this is half composed and half improvised in multitrack format

http://myopus.com/preview/koerberPrelude2.mp3

I will use dissonance in my improvisations but not without using rules.
E.g. I have done a 12 tone row improvised fugue based on the pater noster.
I generally improvise before mass or during the middle of mass I very rarely improvise a postlude.
I try to use dissonance in a pretty way and not an ugly way. Such as when creating natural sounds.
I generally choose a theory around using my dissonance such as resolving to or from a dissonance.
Something I learned was that with use of dissonance there must be a hook if you want it to remain relevant to the choir or liturgy.
It might be a fanfare sound for Christ the King or it might be the intoned section of chant or it might be the entire melody of a hymn broken into sections.
Something people really seem to enjoy is my improvisations. I am not much of an organist. I certainly don't have a ripper technique. But I have a few go to methods and hooks I use both from a consonant and dissonant perspective. I wouldn't ever combine wild dissonance with wild rhythms such as really odd syncopation but I would associate dissonance and consonance with affect.
Depending on the harmonic system I use a 2nd or 7th may be more consonant than a third or sixth with resolution to unison or other perfect intervals. Whilst other times I use the typical 4-3, 7-6 resolutions.
It really depends on the style and the liturgical character or text I'm trying to highlight in my playing.

That being said, I don't like the sound of wild dissonance and wild rhythm and wildness. Mass should give one solace not a heart tremor...
Great concert work though. Just... if it ain't beautiful I doubt it belongs.
It would be like putting in cubist artworks for the stations of the cross... missing the point of the stations. Improvisations are to be realistic and enhance what is going on not to distract from what is going on.

I rarely need to improvise anything and tend to use works by good composers, instead. However, I have heard many of those clashing, crashing, discordant improvs that seemed to me to be nothing more than noise. Like Jes indicated, if it ain't beautiful it doesn't belong. If it edifies rather than shocks, it is on the right track.

A couple of striking processional improvisations from Notre-Dame, Paris, by Messrs. Latry & Lefebvre:
https://www.youtube.com/watch?v=g4RSL8Fn7nk
https://www.youtube.com/watch?v=hZ-pZp1FQPE
Quite "wild" but much more to my taste than that of Baker!

@Richard indeed I understand the confusion here for music is an abstract way of expressing the real.
If you look at artworks such as paintings as the slightly less abstract art form of portraying the real you see that cubism or abstract expressionism differs greatly from say the pre-raphaelite style. The same should be said about music but sadly isn't.

There is cubism that is nearly impressionistic and can clearly be linked to something recognizable and then there is abstract cubism which goes out of it's way to look barely recognizable.
I firmly believe that improvisations should be either setting the scene for what happened in the gospel (which is more impressionistic.) Or should be revealing the melody of the upcoming or previous chant/hymn. This could be done very loosely by following the key. Or it could be done by using excerpts to create a fugue. Or it could be an elaboration extending the melody. It could even be by following a meter or contour line.

When I think about say... the credo... I try to find a poignant part of the Creed that is drawn out in the gospel as this is a chant that people commonly know. So, let's say it's Christmas and we want to point out that God became man, you might pick out the short snippet of melody attached to the words et homo factus est and play that melody in a few keys and harmonise according to affect of the harmony. Maybe you're playing this and the priest in his homily was discussing the murder of the infants by herod. So you might put in a counter line which is haunting and discordant but echoes the chant excerpt you chose.
In the short time between the homily and the creed I might then go on quite the journey using these motifs but there is a reason behind my use of dissonance in this instance and it's not without the hope.

That is making the real by using the abstract to create impression or expression of the real or the truth. In liturgy we have the tangible, historic and the mystical and this is why music is so great because it can portray a little of each.

Motets aren't devoid of dissonance. Think about "Christus Factus Est" and the dissonances which paint the setting of the horror of Christ's crucifixion but consonance that reminds us of the hope of salvation.