Unlike a lot of my friends, my favorite computer games are generally RPGs. Most of my friends are really into first person shooters. I don't even own Halo! I have enjoyed some first person shooters. Way back when, I really got into Star Wars: Dark Forces. I'm a sucker for Star Wars though :-) The games I really enjoyed growing up were games like the Ultima series and Bards Tale on my old Atari 800, and later games like Dungeon Master on my Atari ST.
On the XBox, there have been a few multiplayer RPGs that I've been able to talk my wife into playing, like Baldur's Gate and Dungeons & Dragons: Heros. They've been pretty fun, and I like that my wife and I can play together. However, the game that I've really loved beyond all others is Star Wars: Knights of the Old Republic. It has a very complex story line and it really sucks you in. I couldn't tear myself away from it until I finished. I loaned it to Rob, who thought it was totally lame. :-)
I also love to play 4 player games with friends. Some fun ones are Fusion Frenzy and Whacked! I recently got the Mario Kart inspired Crash Nitro Cart. It has nice graphics, with support for 720i. But, we haven't had a chance to try it out with 4 players.
Now, there are a couple of RPG's coming out for the XBox that sound incredible. The first is Sudeki. Sudeki is anime-inspired and looks to have awesome graphics, and early reviews are very positive. It should be released on July 20th. The second is Fable, due in September. I mentioned Fable a few months ago because of the Danny Elfman score. Major Nelson was sucked into Fable by the storyline, and of course the awesome score. It sounds like you can choose a path of good or evil, like in Knights of the Old Republic. Unfortunately, neither of these are multiplayer, but I don't think that will stop me from enjoying them :-)