When I got MW2 as a Christmas present last year, I was amazed at how good it was - enthralled by the graphics, storyline, everything. I thought, "No game could be better than this".
That is, until I played Just Cause 2.
I've only had it for two days, but already I can see it outranks MW2 in nearly every way. The storyline is much more gripping and exciting, there's a massive, fully explorable environment, and missions so intense they leave you sweating. Another brilliant point is the humour - some characters are okay-ish, but some characters and cutscenes are downright hilarious. The game gets a bit repetitive sometimes, but trust me, you'll be having too much fun to notice.
So, if Infinity Ward thought they made the best action game ever, I say to them, "You are wrong, sirs. That plum goes, and rightfully so, to Square Enix".