Black Flag was a good port. Never had a problem with it at max settings. GPU usage stayed near 100% the whole time(meaning no weird frame rate drops) and never had a bug.
They did actually patch a bug in towards the end so that it was impossible to start one of the missions. Had to download an earlier version of a file for the Principe map and replace the updated one so I could complete the game. Other than that I thought it was great and pretty flawless tbh. Loved it and can't wait for Unity and Rogue.
JR