Good old game.
Quake 3 engine as far as I remember? And not quite impressive graphics, especially for those who are used to shaders and can't imagine a game without high-res textures and high-poly models.
Level design is great however, and music is great, as well as the overall weirdness of what's going on. It does get a tad too complicated from time to time, but generally it's fun. If you don't mind dated graphics
