I hate relying on walkthroughs for this kind of information. There's enough diversity in the floor patterns to allow the use of a contrasting texture for such things, and it would be a step in the right direction. Speaking of items, secret areas, and for that matter creatures killed, you get a display of the various numbers at the end of the level. This isn't optimal. I'd have loved to have gotten information on how many creatures and items were left in the area before I ended the level.
Sound effects are brilliant and well-used.
There are several variants on many SFX clips to keep them from growing repetitive. The worst part is the ending. Even the last FMV has this display at the top and bottom. Someone has suggested that if you get all the Secrets you may get a different ending, and I'm trying that now. And that's a hardware limitation, I'm certain.