There was one fight against a boss that was a huge pain in the ass because he tackles you just as you exit a door to the roof and if you don't use the right maneuver, blam! you have to restart and listen to his monologue. Again and again and again. Dear gods, it was so bad it's actually the only thing I remember from the game.
Which is a damn shame because it really was revolutionary, the architecture is fantastic, and the parkour is flawless. Even the "you don't have to fight" thing was genuine! I literally did not fight a single guy... until that damn roof, where I suddenly had to learn the parry maneuver the hard way. Shame.