So far it feels pretty great. It's not particularly hard (on the highest difficulty), but that would be better left for modders anyway. The rules of engagement are certainly not JA2, but that's not really a bad thing.
I don't mind a large step away from realism in general, but still I'd rather have it in check in certain particular moments (like enemies showering you with unlimited shots while providing absolutely no loot when dead). But again, I understand considerations that were leading to that - any kind of "true looting" would return us to JA2 times again, where it wasn't even remotely possible to run out of ammo enemies were using. On the other hand, the "parts" abstraction works pretty okay for the crafting/modification purposes.
Some game mechanics feel somewhat undercooked - like sound alerts, firing small firearms won't aggro enemies literally 50 meters away? Really? Mines exploding from bullets but not from grenades? Grenades themselves blasting down walls but at the same time not displacing enemies? People throwing knives like bricks?
But those are pretty little things; in general the combat feels quite good. I'm sure that with more patches and balancing (and maybe mods) things will turn out perfect.
PS: Not sure why people are making big fuss over, say, weather effects. Fog DOES reduce vision range pretty heavily (along with grazing mechanic), like it should. Not like it matters too much when you're having Livewire in your team, but it does.