The developers of Crysis, Crytek, have specifically said that Crysis isn't possible on the PS3, at least in a fully optimized form. Obviously, the game could be toned down some, but a full version is only possible on high end PCs. Quad Cores only, basically.
Not with an identical game engine, with a PS3 specific game engine IMO the game can even be greatly improved on.
Note that ID software also claimed Doom couldn't be done on the Amiga at all (granted its game engine approach wasn't very suitable for lowend Amigas), yet the moment Doom's source code was released the game was ported to Amiga specs I owned at the time of Doom's release. IMO take such comments with a grain of salt. (Needless to say ID Software's Quake eventually also got officially ported by Clickboom to 68k Amiga configs available at the time of Doom's release).
I remember telling some people that the Amiga was a lot more powerful in the good old days. They wouldn't believe me as some early games ran better on the Atari ST. They would never believe something like this would be technically possible on a lowend Amiga 500 at the time (the early NES heydays):
Lion Heart videoDisposable Hero