Admittedly this is my first Assassins Creed. From what I played the game has gorgeous environments, detailed characters and robust character interactions.
Unfortunately I felt like the missions although fun, seemed repetitive and not much variety. Its always sneak here, assassinate person X, or sink person Z's ship. The story and visuals really pick up this games slack and mask a lot of its faults. Another thing that irked me was the repetitive nature of the side activities on the islands. Its always collect X amount of animus fragments, loot X number of chests, etc.
Another complaint is the character movement. I expected the character movement to be very precise with almost zero glitches given assassins creed reputation. Boy was I wrong. The sprinting feature feels clunky and a lot of times I found Edward grappling onto edges I didn't intend.
I didn't play too much of the multiplayer but it seemed average. The hunter/hunted mode was fun but not nearly enough to keep me engaged. I didn't even bother with the clan feature as not enough people I know bought the game and there didn't seem to be a lot of folks online.
Overall fun pirate theme, good graphics, commanding a ship is fun but average gameplay, repetitive missions and side missions and lackluster multiplayer.