According to digitalfoundry, the game dips to 20 frames per second on many occasions.
http://www.eurogamer.net/articles/digitalfoundry-2014-assassins-creed-unity-performance-analysis
I call that unacceptable.
To each his own I guess.
Having played the game for a few hours and being amazed by how wonderful a game world I am able to walk around in, how beautiful and detailed, wow. It's, for a lack of a better word, much like an open world Uncharted at times, but more realistic looking. Framerate isn't nearly as much of an issue as people make it out to be. Sure it would be nice if the framerate would be rock solid and I hope they manage to improve it, but people shouldn't let it get in the way of how amazing the game looks regardless.