I just finished Crysis for the first time. God damn at the bugs, at first the last level kept crashing, then I kept falling through the floor, one time just after defeating a boss...
Anyway, I'd say the games are about equal overall now that I've finished both. Crysis has more open levels but it also gets rather restricted as you get closer to the end. Although that wasn't as annoying or crap as I saw people complain back when it first came out. I didn't mind the aliens and the alien structure zero gravity bit was cool. Crysis 2 has some nicer on foot set pieces, COD-like. Crysis had some awesome vehicle sections. I loved piloting that aircraft thing and the tank battles in that large open field. Crysis 2 had some nice more open sections too though, like Eye of the Storm. Stealth is overpowered in both games, I just skipped past 4 armored minigun dudes that kept owning me at the mine entrance in Crysis. So, yeah. Fun games both. I enjoy the Nanosuit 2 controls more personally, but like the open levels of Crysis more.
The bigger difference, I guess, is that I can now try to find and enjoy some Crysis mods that will expand on that fun, while I have to wait for paid DLC for Crysis 2... Also, Crysis 2 runs a little better while looking better for me. I have to reduce Crysis settings much more for similarly acceptable performance. But that's just my crappy outdated PC.