Yeah well, when you have to write 24 songs for the same project -- and thus have them thematically connected somehow -- some of them are bound to be really similar.  Most of these songs are written on the same scale -- except for Paradise Star and Clockwork, which are in harmonic minor... and there are only 12 keys -- so that's at least half the songs sounding like the other half.
It works though, by enforcing the actual theme.

Besides the entire gimmick of the soundtrack was that none of it was 'written' per se, it was all improvised on a keyboard synth and then mastered.