I really kind of hate many things about Unity, but I thought the combat was really good compared to what the series has been for several years now. All of the flashy instant killing was really awesome in Brotherhood. You felt super powerful and it just looked so damn cool. But instant killing my way through four straight games got very old. Combat began to feel like a total annoyance because there was no challenge to it. Getting swarmed by enemies began to feel like a tedious waste of time, because I knew I was never in danger.
I quite enjoyed feeling underpowered for much of Unity. I didn't upgrade my Assassin very quickly which meant I had to be careful about who I chose to engage, rather than carving a bloody path through the entire game like you can from Brotherhood through Black Flag. I found the counter system in this game really satisfying, even if slashing an enemy 5 times with a sword before he goes down is still silly (and let's be honest, that's almost every game that has swords or weapons of any kind).
Also, I disagree that there aren't any cool kill animations. If anything they're way more brutal in Unity!