After playing this game for only a few hours, it is obvious that the game was not ready to launch. The frame rate lags during Ubisoft's much touted sections in large crowds, people literally fall down from the sky into place in the game world, and NPCs sometimes bounce up and down for no reason. During cutscenes, textures pop in and out EVERY TIME that the camera changes to a specific character. This is surprising to me, as the game looks absolutely gorgeous. The textures on the clothing (when not popping in at random), streets, walls, and scenery are incredible. The sheer mass and power of crowds really give the impression of a city in upheaval. The lighting is incredible, and I have had some really amazing moments doing the most mundane tasks in an AC game, such as climbing up to a viewpoint on one of the many incredibly detailed Parisian landmarks.
But in some ways, the gameplay has taken a step backwards. The pathfinding is awful. Arno is fluidly and naturally animated, and the addition of downward parkour is sensible and looks fantastic... when it works. I've been pulled right out of those aforementioned amazing moments by pathfinding issues. Arno will suddenly get stuck on an area of a building for no reason until I move the controller around for a bit, at which point he promptly does exactly what I wanted him to in the first place. Furthermore, while traversing on the city's free-running paths, it is very likely that Arno will not take the path you want. He frequently climbs up a little chimney or the side of a building when a path on the rooftop or a bar/flag pole extending from the building would be more natural and faster. This breaks the rhythm of the movement and takes me out of the game.
Even combat is frustrating, as the camera does not show all of the combatants, nor does it give you a warning to counter as Black Flag did if an enemy happens to be off-screen. I had to keep the pace of the repetitive combat as well as fiddle with the camera so that I could see the guys popping in from off screen to take down my health.
I do not feel that I can adequately review the story at this time, as I am new to the game, though I wanted others to be aware of the game's many technical issues.
As a historical set-piece and world to look at, this is a great simulator. As a game, it is incredibly frustrating. Bugs, poor pathfinding, and a choppy frame rate take you out of the action every time you start to feel impressed. At least you can take a cool screenshot for your friends...