Ubisoft Assassinated Itself in Unity
Assassin's Creed Unity began rolling over the earth from 11 November onwards and since then pretty much all anyone's been talking about is its stuttering and glitchiness. The issues are multitudinous. Protagonist Arno falls through the ground and walks through walls. He traverses air. He gets caught in carts. Characters will keel over and levitate sideways off the ground. People lose their faces. That's not even all of it.
Suspicions are that the game wasn't ready for release but that Ubisoft went ahead with its plans anyway. I'm having flashbacks to SimCity.
The normally unresponsive Ubisoft has issued a mea culpa in the form of an official live blog that will update as fixes materialise. (They're reportedly fast-tracking the fixes for the frame rate, the graphics and collision issues, and the matchmaking in co-op.) On top of all of that, the PC version of the game has some special problems all its own. If you own an AMD GPU, it may refuse to run on your PC altogether.
If you haven't bought the game yet, hold off until this is all resolved.