As the title implies, it's definitely the best. Most of the game will be spent on your ship, especially so if you want to complete all the side missions and ship upgrades. The ship controls very smoothly, and isn't plagued by he terrible controls that the AC series is known for when on land.
Plenty to do when you're bored of assassinating. Smuggler's dens, underwater ship wrecks, naval missions and more are all available to complete.
There are only a few downsides to the game. One of them being the story moves at a snail pace and takes a long time to actually get to anything interesting. The characters are all likeable but it spends too much time on menial details. That said, this is perhaps to add some depth to Edward since Ubisoft will more than likely continue Edward's story with a sequel or two. Speaking of Edward, I found him to be the most likeable Assassin yet! Has as much personality as Ezio, if not more, without the brattiness.
Overall, the game does just about everything right with minimal complaints. Only real downside is the do-everything-with-one-button which leads to you doing things you didn't want to do various times.
Side note: Ps3 version runs surprisingly well with some frame drops in some parts of the cities. 1080i too.
Black Flag overcomes BOTH my complete indifference to Assassin's Creed games AND the clunky horror that has been previous pirate sailing games. Bravo Ubisoft!
I'm half way through this and I can't get enough of pirating and plundering. Great fun.
The story is exciting and interesting enough that they don't even need that silly ANIMUS device anymore. They should have cut the lame future story out completely.
My only other nitpicks. The controls are bit overwhelming at first, but they do a pretty solid job tutorializing. The city missions can get a little bit tedious and unrelated. Walking and running around the deck of a ship can be a bit frustrating, your guy is always jumping up on things or climbing the masts when you didn't want him to.