Kf2s engine upgrade was a big leap in fidelity, and it lost some of that unreal 2.5 charm. The gunplay and enemy AI was significantly improved from 1 to 2 - its biggest selling points imo. 2s shooting was fantastic.

KF2 was quite fun but a change that I personally didn’t like was how, during bullet time, the game turned black and white with only red having. I know I’m in the minority here but I didn’t find it cool or stylish and thought it just made things much harder to see. I couldn’t find a way to disable the black and white effects no matter how much I looked.

The robots weren't unsatisfying because they were robots, they were unsatisfying because the feedback from landing hits was designed badly. When the update introducing them was dropped, there was some initial confusion in some of us as to whether we were actually damaging them properly. 

It just doesn't feel like you're dealing damage, it demonstrates the same kind of feedback you get in other games when you shoot an armored part of a target that just deflects the bullets. 

They just needed more juice. That's easier to achieve with blood, sure, but there are horde shooters with robots that do it just great. It needed to sound more like bullets were tearing apart metal and visually showing bits flying off with every bullet.