I was thinking Crysis 2 would be sweet if it had a firefight type mode where waves of aliens come at you. I'm not sure if they can add something like this after the release of the game but I thought I'd put it out there.

YES, YES, YES....THAT WOULD BE SWEET. They will mostlikely say that it is impossible to do now after release. But, it isnt. Just like treyarch said that they could not add any game modes and disable any perks after release on twitter, yet they add the mlg playlist which enables/disables certain perks

I will pay to download this game mode as an add-on easily

Me too! I was playing with a friend lastnight and we both talked about this game mode.

Not a fan of zombies and the AI needs some improvement before a firefight mode would work.

I'd like something more like onslaught from BFBC2, something co-operative with objectives and timed.