Dungeon Siege 3 isn't bad considering it's $20 everywhere now. There's a whole bunch of those games available for download, Warhammer, Dungeons and Dragons, etc. The Marvel UA games as everyone else said are really good, although beware you can no longer buy the DLC characters for either game.
You can get the DLC on-disc for the first one, but you have to find someone or somewhere that has the MUA Gold Edition. Good luck as GS charges $30 for it used vs. like $5 for the vanilla version and it's hard to find. 3rd-party on Amazon starts at $60.
I would stick with 1 as 2 isn't as good, even though it's related to the comics more than the first one. The first one is essentially a continuation of the story from X-Men Legends 1 and 2 from the previous generation. When Raven went to do Singularity and couldn't do MUA 2, Activision had Vicarious Visions, who did some of the ports of MUA 1 to smaller platforms, do the game. They decided to merge the XML and real life universes (Civil War) together and kinda botched it. Not a terrible game, but really disappointing when compared to XML 1/2 and MUA 1.