There are brutes, electrified guys, ninjas. All enemies who you cannot hit directly (usually). That's not considering stun baton and shield guys.
It does have an impact on the combat, at least it did for me. It took some of the 'flow' out of 'freeflow', because it's quite common in combat scenarios (particularly in the late game) that they are more enemies you can't attack normally than there are enemies you can. So when you have to leap over a stun baton person, stun-jump-jump shield people, attack ninjas and be aware that they can dodge, hit electrified guys with a projectile and stun and beatdown brutes, watching out for tackles that could be coming from off-screen, the combat can become very 'dense'.
Even when I'm doing it well it isn't with as much style as in City. In that game the challenge wasn't so much from the enemies themselves, but a personal challenge with regards to how efficiently you could dispatch your enemies. In this I found myself really having to strategically target specific opponents, and that was usually something reserved for Predator sections. As such I found that I enjoyed the dual-play sequences, where you could be stylish and playful, more fun that the harder combat sequences in Arkham Knight.
