You best be trollin'. The AI in this game is both phenomenally stupid, sometimes being unable to climb a simple flight of stairs, and ridiculously cheap, being able to headshot you from a mile away and behind a bush.
Sure, it's beautiful, but the AI would be embarrassing even by 1998 standards, and that kind of ruins it for me personally.
Now, I see a fair amount of people say this but a lot are just lying, while others are being honest about that. I am sure you are being honest, but i must say that the AI in Crysis is a gamble kind of, because some people have problems with it that others do not. The AI is good due to it being able to hear sounds and react to them, their flanking abilities and how they use the environment given that much of the outdoor environment has very little predefined points for the AI to use. That being said, each individual AI character has a ton of actions that are processed at once, so its very hardware dependent (which can end up making or breaking the game btw)
For example, i got crysis when i had my older computer which had a single core. The AI were extremely stupid, to the point of making me laugh, like much of the videos you see on youtube of them walking up to flaming explosive barrels and such. However, i have a computer with a core I7 now, and the AI react fairly quickly to what happens to them, and it makes the game much more enjoyable. The flight of stairs thing you mentioned is still a problem because they are designed primarily for outdoor environments, and all indoors require pathing which does not work to well unless the pathing is very precise, and it was not at all implemented how an AI system should be for indoor environments, especially for stairs (sometimes AI will try to go down the stairs at the same time and trip over each other
Aside from their problems indoors, the AI is by no means bad. Some of the AI has slower reaction times, but that is partially dependent on the class of AI and the idea that they are meant to work in groups. It's also one of the few AI systems that once your spotted they don't always know where you are. They always check the last location you were visible to them in, before entering a search pattern and searching the area for you and eventually returning to normal. They do have very far view distance, but they cannot see through objects (unless they are specifically made in the editor for the AI to be able to see through) such as leaves and bushes. And for the simple hundreds of vegetative objects that are in the levels that the AI make use of without any pre-scripted events at all, Its a well done sandbox AI.
Plus, i believe the AI is designed to be a scared North Korean