I recently discovered the Windows PC recreation of Dungeon Master, Return to Chaos (RTC).
I first played Dungeon Master in the 80s on my Atari 520ST, and it's probably my all-time favorite game. DM was arguably the first realtime 3D RPG, had incredible ~50% sell through on the Atari install base (not sure what the later-released Amiga numbers were), and is an engaging, stylistic game that still holds up today. And Lord Chaos deserves to be in the Villains Hall of Fame (is there such thing? If not, I'm starting it right now).
Eschewing the turn-based RPG tropes of the day, DM bailed on the Dungeons & Dragons conventions and complicated rules to stats that updated based on actually doing stuff real-time in the game world. Monsters are varied, plentiful, and challenging (I think this is where my fear of all things scorpion-esque comes from), and there are a decent amount of puzzles, jokes, and brain teasers throughout. And leveling up is rewarding and makes a difference.
Wayne Holder, Doug Bell, and the other folks behind FTL Games and Dungeon Master are seriously impressive. So's this George Gilbert guy, who recreated the game "mostly as a work avoidance tactic in my final couple of months at university" (I can respect that). RTC includes not only the original Dungeon Master, but Chaos Strikes Back, Dungeon Master II (I'm admittedly not a fan of that last one), and a dungeon editor -- all in a 12MB download.
For non-Windows folks, there's (in theory) a Java version, but I've never gotten it to run (and I debug Java), and versions from other folks for Windows/Linux/Mac/Pocket PC.
If you have a chance, you owe it to yourself to try this game out. Seriously, finding this port has pulled me away from finishing Lost Planet on the Xbox 360.