Oh and GTA? Fun... to a point. But it's not Mount & Blade! *kills GTA character with Heavy Balanced Bastard Sword*
I think the most fun I had in GTA (San Andreas), was looking for things in the game that didn't really exist (Big Foot, chasing UFOs, hunting sharks, ghost soldiers, etc.

).
I agree that M&B has far more staying power, but you have to remember that GTA is basically a linear game with the illusion of free form play. Once the story line missions are done, there is little but self made mayhem left (I haven't played the new one yet, but the side missions in the old ones never really interested me much).
------------
The only other game, that has stayed on my computer as long as M&B, was Morrowind ..... So that should say alot to a certain crowd

.