Full 3D, like KF/AF, no stats...hmm.
I don't think it's the game you're looking for, but maybe take a glimpse at
Dawn of Darkness, a Quake 2 mod that might have been distributed as a standalone at some point (probably the mod combined with the Quake 2 demo). It might jar another memory loose. The one you're thinking of was graphically cruder, right?
Do you remember where you got the walkthrough - GameFAQs, a more obscure site, maybe something that came with the game?
What about melee combat - simple sword-slashing, or something a bit more dynamic with multiple kinds of attacks depending on your actions?