Okay guys, I'm about 7 hours in and this game is pretty awesome so far.
The pirate theme really clicks with me, there's something incredibly satisfying just sailing the open seas. It's a remarkable feeling and I can't believe no one ever thought of this before. It's just so cool to sail around, spot an island, get close and just jump off your ship, explore the island and find some treasure, swim back to the ship and have your men cheer when you climb back on board.
I just unlocked the Homestead and the fleet mechanic, which is essentially the same as the Brotherhood "send out your assassins to parts of the world to do missions". But it works really well, it's fun to manage and entirely optional.
The game introduces new stuff really gradually, as opposed to ACIII's "here's a bunch of shit to do. You can do them or not I don't give a fuck".
Another thing that really stands out for me [and this is a total pet peeve of mine] is the user interface - menus are super fast and snappy, intuitive and logically to navigate. The aesthetics are very appealing even though I haven't really figured out why.
I did one official story-related assassination in my playthrough so far, side objective was to kill my target via air assassination. So I spent 20 minutes setting up the perfect situation, finally taking the leap and that asshole Edward auto-locks onto the wrong guy and fucking stabs the guy standing right next to my target - who's AI kind of borks while this is happening and is just standing there looking at me like he couldn't believe what the fuck just happened.
In the end I guess the enjoyment of this game is 100% dependant of wether or not you like the pirate setting. The core gameplay is still as stupid as ever with shit stealth, shit eavesdropping and shit scripted mission segments that 9/10 times pan out wrong because the AI messes up somehow.