Black Flag is one of my favorite games of all time and sadly this is a weak spinoff. Its short to the detriment of the story despite a really interesting premise. The Abstergo segments are slow and plodding and don't really add anything new to the lore. The trophy list is also quite poor with several trophies just being a nonsense grind because the world is so much smaller than Black Flag that they just wont happen naturally.
In short: its just ok