I've just finished it, so here be my thoughts:
WARNING! SOME SPOILERS BE AHEAD!LIKESEzio Auditore - It's sad that this is Ezio's swansong from AC, but what a journey it's been. From his birth to his reckless youth up to his rise in the Assassin order, Ezio's life has been a bountiful playground for us gamers. And some of his finest moments are to be found here. There's the fantastic action set pieces showing that even in his late years he is still very much a badass. We also get his humorous side in the bit where he infiltrates the Sultan's palace disguised as a minstrel, with hilarious results.

Then there are the quieter moments, such as his growing romance with Sofia Sator that provide a sweet respite from all the death that surrounds his life, and show us a softer side to his character. At the end of the day, I think Ezio will go down as one of the greatest protagonists in a videogame in any generation. It's been great playing as him, and I will miss him.
Altair Ibn La-Ahad - When last we left Altair in AC1, he'd just killed his former master and taken control of the Brotherhood. But for much of the game, he was an arrogant douche who rubbed people in the worst way. So it's refreshing to see him develop into a kindly and wise mentor to the Assassins in the Masyaf memories. Some of the series' best moments are to be found here. From his tragic exile after his wife is killed to his triumphant return to take control of the Order once more. His final days are some of the most touching moments I've seen in a game.
The Ottoman Empire - In AC1 we stumbled through the Crusades, and AC2 and AC Brotherhood allowed us to fool around in Renaissance Italy, so it's great that this game allows us a chance to explore an historic empire not often featured in any media. Constantinople is a great city, probably the best Ubi has designed for AC. And the characters who populate it are interesting. Like Yusuf, fun loving leader of the Constantinople Assassins to Suleiman the Magnificent, though only a teenager here is already showing signs of his future greatness.
Action aplenty - Despite this game being the last hurrah for Ezio, it's no doubt his most intense outing. There are a ton of spectacular set pieces to be found here. Of note are the two of the Masyaf key missions to the final chase. Ezio's probably the closest we'll ever get to being Zorro in a game.
DISLIKESStill too many questions - Despite it's title, the game doesn't really reveal much and just acts as a bridge to the next game.
Engine showing it's age - While I'm grateful to Ubisoft for cranking out game after game while not sacrificing quality, the AC engine is starting to show it's age. And it's not just the graphics. Some gameplay issues that need to be addressed in the sequel. Such as combat, which is not smooth as is should be despite the Kill Streak mechanic. Free running also needs a bit of an overhaul to make it a much smoother experience.
Desmond's memory bits - Argh. No first person platforming Ubi! I dislike those immensely.
Janissaries - Ugh. These ****holes are hard to kill.
All in all, great game. Not as good as Brotherhood, but it being Ezio's swansong more than makes up for it.