The CD version of Schizm is actually 5 CD's.
You're right. It's on 5 CD's. I misspoke.
I have this game but (of course) never played it. I think I bought it used.
It's sort of a Riven-style game -- difficult but with logical puzzles. Harder than Riven I think.
Never played Reah either and don't have it.
Reah wasn't as good puzzlewise, and there were places you could be killed without warning.
Both had interesting architecture, as you can see from some of the screenshots. The living "ships" in Schizm looked amazing back in 2001 at the time of release.