Just bought this game recently and played it on my macbook pro 13" i5 2.5gz 4gb ram and standard Intel HD Graphics 4000 512 MB.
Game worked perfectly (although not on the highest graphics but it did not look bad at all :D), very little lags which did not severely hamper the gameplay. Mac got a bit warm but nothing extreme.
I totally recommend it because it is a very fun game to play. just too bad that you can not actively travel between cities because the main part of the story takes part in rome (btw, Rome is huge)