Hold off and get Bully, or REALLY hold off and get GTA IV or Smash Brawl.

Army of Two is supposed to be good, but only if you have Xbox Live. From what I hear, it's super short.

Bully is about a 20 hour long experience

Quite funn though,
on IGN.com...

Bully: Scholarship Edition- Rating- 8.7
Army of Two- Rating- 8.7