Having trouble deciding what game to buy

[Prash]

I have a £40 voucher. I really want a nice mac game but don't want to buy one and regret it.

I'm really into online games I love playing with real people. So things like counter strike: source

But I'm open to any big name games like Deus Ex but prefer the online community.

Any suggestions which wont leave me disappointed?

 

[AFPoster]

Diablo 3