Actually, they do have thermal vision.
When you're inserting an AI grunt in Sandbox, they have a ThermalVision switch in their AI options. And boy it is overpowered, so these Crysis mods that improve AI realism usually switch it off for heli pilots.
I enjoyed Crysis very much. In fact, it was one of the 2 main reasons I upgraded from my old 6600GT setup, the other reason being TES IV: Oblivion.
Crysis SP has quite some replay factor for me, especially the first missions before the Alien plot really starts.
My personal favorite is the part when you secure the hostage from that school; I love replaying that part (I play stealth on Delta). When the Koreans get to know you're inside the school building, but they're not sure where in the building you are, they'll start crowding near the stairway (assuming you didn't shot them down before).
What you need to do is to sneak up to them on cloak, and gently punch someone in the foot. Then watch them collapse like dominoes, tumbling down the stairs and shooting randomly in panic. Another way is simply throw a grenade inside the crowd and watch the flying guts but I'm not the Postal guy, I prefer the 1st method, and it's way funnier.
Multiplayer is alright too, and I spend quite some time playing it a year ago. Maybe it has only 2 game modes, 3 in Wars, but it's still fun for me. Maybe because the only other game I ever played online was MW4 Vengeance :>
I agree that Crysis was in fact a tech demo for CryEngine2, just like Far Cry was for CryEngine1, and Crysis 2 will be for CryEngine3. But what's wrong with that, if it's a good game with mind-blowing visuals?