Ecks vs. Sever info please!?

[Gamer]

Hey i am thinking about picking up a copy of Ecks vs Sever, just wondering, first of all, is it worth it? It looks pretty cool and probably better than the other few shooters. If someone could give a brief summary of what the game is about and what there is to do in it, like how many missions, what type of options there are that would be great! Thanx a million!