Funnily enough I listened to the Interstellar soundtrack earlier today, but I tried not to let that color my listening experience.
For a start "didn't really work out at all that well" is probably a bit an overstatement, though we tend to be our own worst critics! There are chunks of the piece that do have a nice sound to them. 01:05 - 01:45, has a nice blend of choral arrangement, with the organ just placed right in the mix, with some meaty clicking and clacking adding a little rhythmic spice. Texturally, it's definitely got something going for it. Mix-wise, consistently solid throughout.
In terms of detractions, I don't think it's what you tried sound-wise that "didn't work", to me it's the more basic structure of the piece. The only element that didn't work for me in that regard was the french horn at the end, didn't feel like it was sitting easily in the mix, and the line it was playing was weak.
Structure-wise, the chord progressions don't really develop enough to hold much interest and combined with only very shallow dynamic changes, the whole piece feels like it's in the same register and tone - basically pleasant, but without really taking one on a musical journey. For a piece which relies heavily on texture, I think you need to have the dynamics be a lot more interesting to carry the listener through.
In short, I think what you were experimenting with actually worked better than you thought, it's the basic musicality actually that could probably have done with some fleshing out.
Had a wonderful time Mastering this, as always good work, Musical suggestions: Your choir-using work is excellent, but if you could maybe work on making it more of a frontpiece, possibly make it more varied, more lifelike pitch-wise, it'd be that much more impressive. Latin phrases have a lot of possibility because chopping and cut/slide editing can maintain grammatical correctness while playing on the sample for originality. I'd love to see more brass solo stuff like the ending as well, possibly go faster with the horns, something rushing and exciting. You've got the cinematic epic down, spread out.
Please contact me if you would like to use this in a project. We can discuss the details.