Some may disagree with this making the list, saying it's not really in the same spirit of other first person shooters on this list. (fraghero.com)
It encourages players to work together in a group, something I have rarely ever experienced in other first person shooters. (segabits.com)
So how good does a first person shooter need to be to make you by other first person shooters if you didn't even like them in the first place? (n4g.com)