CrYzZer, good luck with Freeth.

The Cave is an awesome concept for an FPS. You will be able to use the lighting to really bring the player into the game and add suspense. One of the things I like about the idea of the cave is the player constraints that you can design into the levels. Done well, you will be able to totally disorient the player. Adding crouch and prone crawling to the normal walk, run, and jump motions would be great too.

Cheers,