I put off playing Crysis for quite a while but I started really putting some time into it a few days ago. I'm just about to the end (carrier is being attacked) and I have to say I'm completely impressed.
The flying mission kinda sucked (due to the backwards flying controls that can't be changed), but even on Delta the only level that really gave me any big problems was the first fight with the Korean nano suit guys in the swamp. I lowered the difficulty just for that battle and then put it back up to Delta afterward.
I have to say, I couldn't stand Far Cry (what little I could get myself to play) but this game is just blowing my mind. It can be frustrating some times, but its just so damned fun! I actually thought the zero-g cave levels were awesome. It was a little disorienting but the visuals and the sounds were just amazing (as with the rest of the game) and it was an interesting break from all of the hiding in bushes tactical stuff.
I really thought the game was going to bomb completely after the first half like most people have said, but I've enjoyed it from the beginning all the way to the end (well, almost the end).
The production values on this game are just out of this world. I really don't expect to see another game with this much complex, varied scenery and effects for a very long time. I know visuals alone don't make a great game, but good solid gameplay mixed with ground breaking visuals certainly do.
Sorry for foaming at the mouth, I'm just completely impressed. Maybe all the negative crap I've read lowered my expectations, but this is a hell of a lot more than I expected from this game.
Hopefully the last level(s) are as good as all of the ones up to this point.
EDIT: Also, FINALLY, a game worth upgrading for. This is one of the few single player first person shooters I can see myself replaying in the future on better hardware.