Crytek have made their name perfecting tropical environments, and their games are specifically geared to take advantage of them. They can't simply change the background and hope the rest falls into place; in order for Crysis 2 to work on the same fundamental level as the original, the action will need to change too.
This could bury Crysis, or it could morph it into an entirely new game, one that PC gamers and fans of the original might not be happy with - chatter that it's 'dumbed down' for the sake of consoles is going to be difficult to shake off - but one that's right at home on 360.
So, there's a mountain of worry, but there's plenty of hope, too. Without playing the game, and based on the small amount we saw, it's difficult to tell if the tech videos Crytek showed paint an accurate portrayal of the game - but CryEngine 3 shows huge promise, and Crysis 2 has enormous potential. It might not be the sequel we were expecting, but that doesn't necessarily mean we're being cheated out of the Crysis experience; just that Crysis 2 may offer something different.
And if that something is leaping between buildings in a single bound, punching soldiers off rooftops and crushing cars beneath our super-powered feet, then it's a change we think we can live with.