Assassin's Creed IV: Black Flag:

I completed most of the missions previous week.
All it was left for me to do were destroying Legendary ships and messing around with Kenway's fleet.
These four naval battles were bosses of sort and on top of each of the ships being tougher AND faster than me they all had their special gimmicks. It was a good thing because by the time you usually start to beat Legendary ships you are way overpowered for any other ships in the Carribean.
HMS Prince is always in the fog or a storm, so you're always fighting her and the elements at the same time.
La Dama Negra spams you with her insane mortar power, but if you manage to get in up close she is easily dispatched.
Impoluto
LOVES to ram you, so you need to stay away from her and keep spamming mortars.
And finally the hardest of them all: HMS Fearless and Royal Sovereign:

Two legendary ships at the same time, each faster and tougher than you. You will need some very careful manoeuvring so that they wouldn't surround you from both sides.
The right strategy is to be constantly turning so that you wouldn't get between them and keep ramming and shooting at one of them.
Once one of the ships goes down, remaining one changes tactic and basically turns into Impoluto ramming you like nobody's business. This part of the battle is just as hard because last ship is
still faster than you so she will always get to you no matter how fast you're trying to ran away from her.
After i collected last treasures i found out i am still one treasure away from 100% sync. Apparently one last treasure map is unlocked through Kenway's Fleet mini-game:

At least by this time i realized i can send more than one ship... That made battles a bit more interesting, but not really.
Kenway's Fleet is still the stupidest and the most boring part of the game. Doubly so, because in the best traditions of Free-to-Pay mobile games it has arbitrary restrictions by time: once i sent my ship i have to wait 10-24 hours until it "finishes" it's mission.
So, in the last 5 days all i did was -- booting the game in the morning and sending more ships until finally this morning i unlocked the last treasure map. Then a quick dive into underwater smuggler's den and i have full 100% sync.
Overall:
Great game. Around on the same level as ACII or Brotherhood. Decent story and lots of stuff to do. Diversity of mission is probably the best among all AC game so far.
Full sync requirements are MUCH more relaxed compared to previous iterations and that is a HUGE plus if you want to 100% these game. No more retrying the same story missions dozen of times just to hit one particular requirement at the very end. Also, sync requirements are removed completely from side missions so that's an even bigger plus -- because in previous games the most insane and broken FS came from these missions (most of the vehicles side missions from Brotherhood were impossible to full sync, not just "impossible" as in "really hard" but
actually impossible due to broken AI).
The game basically is divided between naval stuff and normal assassin's stuff. Naval stuff dominates over usual city roaming gameplay a bit too much though. And there isn't really all that many cities to roam around in.
The only city that is even comparable to cities of II or Brotherhood is Havana but even that is fairly small. Most of other walking space are island villages, jungles and lots of small Wind Waker style islands with a single chest or on it.
At least Havana and jungles provide a welcoming change from ACIII's bland cities and forests:







Then there are sea missions:


The first moment where you zoom out to travel speed and your crew starts to sing shanties was very cool.
RPG progression with ship was a think a mistake -- it made sea battles way too hard in the beginning and way too easy in at the end.
And the only way to upgrade your ship so is by spending metal that you can only get from sea battles. So it's a vicious circle of grinding levels with easy ship until you become overleveled.
One trick to i used a lot to defeat several ships at once was to get some damage to a big ship or a fort then destroy a small ship and board it:

When you start boarding sequence all enemy ships graciously stop attacking you and wait until you're finished. After you finished boarding you can choose to repair your ship and continue damaging other ships.
I would actually preferred if they kept naval battles system from ACIII because there was a bit more skill involved than just "be level 40 to defeat this ship or get lost".
Story and sci-fi elements:
Did i mention i LOVE sci-fi? I always liked modern parts of AC and sequences where AC got weird with "First Civilisation" stuff. I LOVED creepy puzzles from ACII and Brotherhood and i loved completely out of the blue ending of II.


Black Flag develops AC: Liberation's "Abstergo Entertainment" idea where they pretended Ubisoft is a subsidiary of Templars and that AC games they do is but a side product to their Animus research:

Pretty cool villain too.
The story in the past was alright i guess. I wished there was more of Haytham in the end but what i got was okay too.
So, again, great game. Worth spending 63 hours to 100% it.
Freedom Cry, here i come!