I'm actually downloading Far Cry 3 at the moment on my mid 2011 Mac mini! Yes it has the 6630m but might give you somewhat of an idea if it runs ok.
The Mac mini whilst not being a dedicated games rig is more than capable of playing games no matter what some people will have you believe, as long as you are realistic with your expectations and don't expect to play very latest AAA titles.
I regularly play Counter Strike Source, Team Fortress 2 and Day of Defeat Source on mine (not massively taxing games).
Other games I've played include Battlefield 3 (fairly low settings but runs pretty well), Call of Duty Black Ops, Modern Warfare 2?, Portal, Stalker series, Crysis, Crysis 2 (crap game!), GTA 4, Left 4 Dead 1/2,