I bought Crysis 3 two days ago and started with Post-Human immediately (I always pick the highest).
But I have to say, the cloaking and the bow make things too easy. Its like walking through a museum of dead creatures... The only real threats in Crysis are my own stupidity and impatience, and maybe the Alpha Seth. But even for him I needed only two attempts and only because it took a while to figure out how to kill him.
And I am not even a pro gamer. I play BF3 regularly in multiplayer, so I have kindof a heads start, but that's it.
But maybe this is a general development, because also FarCry 3 (which for some reason I associate with Crysis), was far too easy, even easier than Post-Human. If there is no challenge in a game, then it is not worth playing. And let's be honest, Crysis 3 does not excel at storytelling, its pretty lame. It excels at graphics... Besides that it should also excel at difficulty. You have a Post-Human mode and say "Don't even try". Well I did, and succeeded without any trouble... Post-Human feels to me like maybe the first difficulty after "Easy".
So my suggestions for fixing "Post-Human" (you could leave everything else as it is):
1) Add a patch, rotate back all difficulties by one, so that Post-Human is available again and can be reconfigured.
2) Remove precise aiming for the bow. It is absolutely OVERPOWERED. This is a killing machine. It's no fun. Just add greater bow-drop over distance and remove any aiming assistance, like cross-hairs. Distribute the arrows in a cone, not just a straight line. Make us miss the target more often!
3) Reduce ammunition supplies. There are far too many (Sometimes it feels like one box for each enemy). Post-Human should have more or less exactly enough to survive. Only for End-Bosses you should leave as it is, since you have to face them, and "forced" dying because you don't know how to kill it from the start is also no fun. So you should have plenty of ammunition to waste...
4) Think about at least counting deaths... Or even limit deaths to say something like 10-20. If you die more often it could print like "Nanite source is exhausted, revival is impossible. You are dead!". You could distribute Nanite sources in the game to increase the amounts of revives.
Remember that the good old games, like Super Mario, always had this in them! I think it is sad that these days people are spoiled like this. Dying is irrelevant. You don't need to think what you are doing. Just jump in until you succeed. That svck's and in a way is a reflection of todays society.
5) Make the cloaking less effective, especially AFTER you have been detected. That is also how other games did it. This would add an extra edge for absolute stealthiness You can't seriously sell us that the Ceths are not able to detect their own suit, or at least you get the idea (I am not a Crysis Fanboy, so I am not really aware of the story anyway).
6) Other games bring REAL re-enforcements when you are detected (even FarCry 3)... It was really unpleasant when they found you, because the level got ridiculously hard after that. In Crysis 3, that is missing entirely.
7) Don't display enemies who are out of sight on the HUD. This is too easy. You should need to continuously watch out for them and remember their movements. Nanovision, could still spot them, but svck up energy at least...
8) You said that it is hard to get good AI in the game. Well I can't see it in Crysis 3, so is that what you meant? I mean the enemies are really embarrassingly stupid. There is absolutely no "collective mind" or anything. Just watch at how "The Borg" do it. You are ****, once they know where you are... They adapt to your weapons if you use them too often, and they can adapt to cloaking if you hide with it too often. The same idea could apply to Ceths, since they are quite similar to the borg (from the basic idea). I switch from cloack to armor, shoot one of them with a usual gun, go back a few meters, cloack again and shoot all the others with the bow as they arrive. This always works even though I normally don't have the patience for that... That's lame. AI should try to surround you, smoke you out, block exits, maybe even use the "knowledge" of where you really are, because its just a game and would make AI design a lot easier...
9) Make use of Nanovision and the suit expansion. REALLY, I NEVER used NanoVision and I NEVER used any suit upgrades... So why bother including any of them? Just look at other games, like FarCry 3, which is not a role model, but even this one got it a lot better. Suit upgrades should be essential to the game and the way you play. You should stand no chance without a correctly customized suit that is tailored to your own gameplay (stealth, rambo, or maybe the diplomat "Hey look Ceth, if you don't move out of my way, I will kill you, what you say to that?"). Ah the diplomat is actually quite an idea. Since you used this idea of impersonating the Alpha Ceth in the game already. You could add a role towards gaining control of aliens, with proper customization of the suit.
9) Whatever... I am not working there so you get the idea, come up with more yourself