I like the gameplay depth they have. Theres a bit of luck involved (sometimes a lot of luck), but you can really think situations through and do damn near anything at any time. Close to death I'll drink a potion or read a spell and hope for the best. Sometimes it saves me (woot, teleport scroll!) sometimes it kills me...its kind of fun either way.
You may not care to try them, but if you do, my faves are ADOM, CastlevaniaRL, DoomRL (very actiony), and Dungeon Crawl.