Chasm: The Rift.  I originally played the shareware version of this several years ago, and I liked it a lot.  I'm also a fan of Quake, and although I prefer Quake, I still think Chasm was a good game.  I didn't get the full version until many years later.  I played through the game and enjoyed the levels, enemies, and especially the bosses.  Even for being the "Poor Man's Quake", this is a classic game that I still like and haven't forgotten.