Here's my history with it- played ACII and Brotherhood, loved them both, tried to play III, for bored within a few hours.
So far I'm loving this game. Disclaimer - I love pretty much anything with pirates in it. But it really feels like they made ACII work, the open world feels more open and more full of stuff to do, the upgrades are very useful with tons of high level ships roaming around in areas you need to go to, etc. The upgrading feels a lot like Mass Effect 2 to me, not essential to the main storyline so far, but it helps a lot on the side stuff.
Story wise I'm finding Edward a whole lot more likeable than Connor was, and you don't have to play through hours of him as a child so that helps to not hate him.
I'm liking it a lot. So, that's my take on it. If just depends on your plan for next-gen consoles and stuff. Since I'm a Wii U Owner, this was a pretty big no-brainer.