I agree with the plugs for Mordor and Demise. (For the record its Demise: Rise of the Ku'taan, Decklin is just the guy who maintains it now, but isnt the guy who made it)
Demise is the only real first person dungeon crawl of the bunch, since its the only one that shows more than just a random picture for the dungeon. The games are pretty tough if you dont know what you are doing, and really benefit from the meta gaming min/maxing (mostly maxing) gaming style and are really heavy number cruncher/stat whoring type of games. They are also pretty immense. Demise has 30+ dungeon levels and an expansion coming out or is out, not sure about it. Mordor has only 10 levels but the difficulty jump from level 3 to level 4 is pretty intense, along with from 5 to 6. Mordor 2 is a lot like Mordor 1, with pictures in place of numbers/text. It says it has more levels but it doesnt really work out like that, since every other level is a basicly blank level. Mordor 2 Eventually turned into Infinite Worlds and then that turned into Demise.
Demise also has multi player where you can party up with someone, but in reality it doesnt work so well, and ends up being more of a social atmopshere with people sharing items and monsters in the shop, and when you die they can come rescue you. Single player in all of these games allows you to run a party of 4 characters that you make, but its not a permant party. You can run each char individually, or in a party of others up to a maximum of 4.
Unfortunately Demise has a problem with Windows Vista (64 bit, and presumably Windows 7) where it wont install or run. Personally Ive never had any problems on Vista, and havent tried it on 7 yet.
Sorry for the wall of text, I just absolutely love these games and have been playing them consistently for the past 15 or so years.
The community for the first game is here:
http://mordor.uni.cc/forum/They are also creating a version of the game themselves, although its been taking a very, VERY long time, and is probably no where near release yet.