Just some more thoughts and impressions:
Regarding AI:
I hope all the COD4 lovers realize that there are worlds between COD4 and Crysis AI?!
In COD4 everything is strictly scripted. Enemies come in endless waves if you cross certain thresholds. Sometimes they seemingly pop up behind you in an area they can't have reached realistically. The enemies have zero search routines, or casual behavior they always walk the same paths (sniper mission where you have to hold still and the convoy searches for you).
In Crysis there is a limited number of soldiers deployed on a battlefield and those guys call for backup, use the dynamic environment for cover and advance, they search in teams, they get frightened and they have to travel the normal way to reach you.
If a level has e.g. 30 soldiers they all follow the rules of the game. You can attract them with loud noise and try to fight them off or pick them out one by one.
It's a completely different kind of game and AI.
COD4 is way more arcadey and the enemy waves with hundreds of soldiers sometimes are ridiculously over the top.
Of course there can be some glitches with a complicated AI system like Crysis has. e.g. soldiers running to man a MG and you pick them off and they don't realize that not manning the MG would be a better idea. But I take those glitches before any of the scripted boring arcade stuff of other shooters any day.
Graphics:
Even as someone who normally just runs through games and knows a lot about 3d modeling, animation, texturing I was amazed so often, that the game probably took me 5 hours longer to complete.
Skybox and draw distance:
COD4 has ugly low res skybox image planes as backdrops. e.g. mountains based on some photo source. The problem with this is that you can clearly tell when the normal level ends and the skybox begins. Worse:
Sometimes the foreground 3d objects have LESS detail than the skybox plane. This looks bad, bad, bad.
Crysis is the first FPS that I know of that has realistic scale and draw distance (Far Cry's scale was a little tiny) and manages to draw actual 3d geometry until the horizon.
Even Oblivion with all the high res packs and LOD patches and whatnot doesn't look nearly as good and the sense of scale in Oblivion is more like a toy railroad universe than something realistic.
Crysis even manages this draw distance without having too much annoying textures popping up or other LOD tricks. It all felt very smooth.
Coupled with the perfect depth buffer usage for distant haze and fog and the volumetric clouds, the sun shafts and all the other atmospheric features it is the first videogame to date where you really feel the world and not get distracted by engine limitations.
Just some more graphic/gameplay features that stand out and above the competition:
+REAL snow and rain: The snow is in the actual level and not just blowing in a box around you all the time following you whereever you go (Oblivion)
+Snow & rain shaders are amazing. I took 30 minutes on the carrier alone to check out all the wet planes and the rain falling in the ocean.
+REAL 3d water tesselation not just flat shaded ocean planes and the boats and floating stuff react to it.
+REAL dynamic shadows that are perfectly filtered (hello FEAR)
+Sharks, butterflys, frogs, goats, chickens, birds, fish, crabs, turtles, pastridges, moskitos and other animals which all can be killed, picked up or messed with
+Breakable vegetation with on-the-fly boolean operations where you break stuff
+Driving tanks through a field of banana shrubs and everything breaks and the leaves react to you and the tank (compare that to BF2 where picket fences are an impossible barrier for a battletank)
+Breakable stuff everywhere (not like COD4 where every sequence when something breaks is scripted and small bricks are glued to the ground)
+Oil barrels that have actual oil in them and leak accordingly. When you throw it in the ocean a cloud of spilled oil forms
+Awesome physics system with no cheating. Just one example: I managed to jump onto a hovering VTOL and got a free lift. In other games this would probably have been a scripted ghost object where I'd had fallen through. I then took a barrel and jumped on the VTOL and placed it on top of it and the barrel swayed realistically on the back of the VTOl with every movement WOW!
+Awesome little details like player hands grabbing stuff (hello Gordon Freeman!)
+You can see your body and feet leave footprints in sand and move realistically (hello Gordon "Ghost" Freeman!)
+Weapons customization and possibility to dual wield melee weapons. (during the last level I ran around with Gauss rifle in one hand and Golf club in the other, those buggers never knew what hit'em)