MMORPGs are often ruled by stealthers..depending on who you talk too you will either hear that they are uber godlike or nerfed silly.
Dark Age of Camelot has a lot of stealth characters and they are really fun to play.
Ultima Online also has a lot of stealth potential.
I realize this is a bit besides the games you mentioned, but in the MMORPGs you are up against other people, not AI. That can sometimes add a bit of adrenalin to the mix
