You can PvP in GuildWars 1. Guild Wars 2 will also have that and more, with large scale battle in World PvP.
Do you mean PK ?
I thought Titan's Quest didn't work well because of the lack of a good piracy protection (the game crashes due to the crack). And the lack of dedicated servers (like battle.net) is also a problem, they used gamespy "matchmaking", and the players host the server and it's a real problem if they use cheats, it ruins the game.
Guild Wars came out at the same time as WoW and is still successful, Guild Wars 2 is one of my most anticipated games.