My comments, just as a singer, and without a lot of technical vocabulary, is that I would like the melody to develop in a more structured way working with the text and the duet as 'dialogue'. I think this will help with the problem of "not very interesting".

For example, the tenor has a brief passage with a change of key (27-37) - but this seems to me very brief, and it transitions out of that key rather arbitrarily. Even the opening phrase by the bass (1-20) carries a lot of melodic variation that is nice, in itself, but that seems a bit arbitrary. By arbitrary I mean not linked to the meaning of the text, nor to a gradual development of tension and release in the music.

If for instance, the bass introduces the problem with a simple somber tone (A): I am weak, I am worn...
And then - with a sense of hope in a melodic change (B)(still simple) - petitions the Lord for aid: "Precious Lord, take my hand..." (but maybe he just says it once, to introduce it)

Now the tenor responds, sympathizing with the problem, and using a more elaborate variation on the theme the bass sang in (A): When my way grows drear... and then moves into petition (theme B), elaborating on the theme and growing stronger, with some repetition of the "take me home".

You could even go back and forth one more time before they sing together.

Then the two sing together, first the sorrow (A) with a longer variation on the (A) theme, followed by the prayer (B), longer and elaborated even more, repeated several more times...

Please disregard if not helpful.

CatherineS - Very grateful for the time you spent looking at this piece and giving suggestions! I'm excited to dig in and work out some of your ideas suggested here. Thank you!