The biggest issues at launch were IMO abysmal texture quality, extremely low polygon count on the geometry and the fact that Crysis was no longer Crysis, but Battlefield:Modern Near Future Warfare 2.
Crysis 1 was open world, my greatest memories in that game were being legitimately scared of helicopters and the Korean nano suits because they could kick your ass in a second flat. Also, I had the choice of approaching a checkpoint at any angle and using the environment to my advantage. If I didn't like a particular approach, I could decide to go to a nearby cliff, go prone, snipe somebody on a mounted gun and then relocate. If things got too hairy, I always had the option of running into the water and swimming away until the alarms stopped going off and search parties were out of range. There was an actual challenge, not because like in Crysis 2, some enemies just took so many bullets to down but because the AI would actively work together and hunt you down. There were unscripted ambushes in the forests and t was unpredictable.
Admittedly the alien part of Crysis 1 was sort of shitty though. The Aliens just weren't fun, so what does Crytek do? Nothing but alien meat shields in Crysis 2. IMO, a FPS should not make it feel like you're shooting BBs at things. Challenge because it takes a full magazine to down something is not fun, it's just a shitty grind. Challenge because a squad of N. Koreans are flanking you while you're pinned down by a MG nest is interesting.
Crysis 2 in comparison was small and cramped. The horizontal area was not all that small, but you lost all freedom of movement. You couldn't have nearly as much freedom going up or down. The tactical visor thing was also a joke, it amounts to A) Shoot these guys from here or B) Shoot these guys with this other weapon over there every time, all the flexibility and actual gameplay went out the window. Also, everything was always scripted. You either almost always knew, were told about or could see enemies up ahead, or you ran into a scripted ambush.
Crysis 2 was a lot more action, but with almost none of the tactical gameplay I enjoyed so much, it is essentially Halo in NYC executed piss poorly.