OK, hold on, this is gonna be a long one. Sorry about that. It has pictures tho.
(Please remember, english is not my main language, so please excuse the typos and gramatic errors).
Ezio
I honestly don't know why I like Ezio so much. He's charismatic, yes, but he's also kind of an asshole. I've followed him for three games now and I realize that he's interesting because of his relationship with others: his sister Claudia, his mother, his uncle Mario, his friend Leonardo DaVinci or his lovers Cristina and Caterina... but not by himself.
And that's maybe why I didn't enjoy Assassin's Creed Revelations so much. He no longer has his aquantaices at his side. The new characters are too simple, their relationships too forced or uninteresting. Even his new romantic interest, Sofia, is just a damsel in distress, even a little worst because of the difference in age between the two.
It's a shame because this is the game that closes Ezio's story and doesn't have anything insteresting to do with him. He doesn't have an arc. He's the same person when we reach the end of the game (just with a new girlfriend). The revelations about Altaïr's life have, ironically, few revelations in them. The information dump about the first civilization at the end has no relation at all with the adventure we just had.

Constantinopla
My first impresion after arriving to Konstantiniye was awe. I was amazed of the view of this gilded city, with the sun reflected beautifully on the waters of the golden horn. Edifications like the 'Hagia Sofia' impacted me with their design and I couldn't wait to explore it all. And then the love at first sight died, because this city is no different from Roma in AC:B. Despite the ports, it's incredibly similar in their design and the visuals are not enough to make a different impression. I grew bored of the city fast. How could one of the most important places of the Ottoman empire, the jewel of the islamic culture of the XVI century could be so uninteresting?
A few excursions to a cave city in Capadioccia and Masyaf did little to add some variety. Anyway, I did love one thing about this representation of the middle east: the costuming. The clothes and outfits on the people that roamed the streets, were peasants, soldiers or royalty, was amazing, as usual in this franchise.

Game systems
I liked Assassin's Creed Brotherhood. A lot. But I remember describing it like an overly long DLC of Assassin's Creed 2. It has new cool systems, specially the recruiting of assassins and the way we could summon them to help us or sent them on missions. AC:R plays exactly like its predecessor with a few minor additions, like the hookblade, that allow us to make a few extra moves in battles (nothing important) and traversal, like sliding across cables. This seems like it would make movement more dynamic and fun, but there are really few places where is useful. The same can be said of the new parachute.
A new mechanic that was heavily marketed for the game were the bombs. Now you can craft and use a lot of types of bombs with different effects to kill, disable or distract enemies... but I found that they weren't that useful after all. There are a few specific situations where a well placed bomb could avoid a fight or make it easier, but most of the time it was just easier just fight, summon the assassin's or use a guild. The city is full of materials to make this bombs, but I stopped used them so this discouraged most of the exploration.

Chasing trends
There is a 'tower defense' minigame in Assassin's Creed Revelations. It's awful. the pacing is so fast that you can strategize how to place your resources and the view of the battlesite is extremely limited. You can even use an overpowered cannon to not loose. The designers had to knew this was bad, because you can only access it if you play careless. That's right, this minigame is a punishment for the player.
Why it exists? Ubisoft is the kind of company to "throw everything to the wall to see what sticks". AC:R was developed during the tower defense fever (specially Plants vs Zombies). They probably spend so much time developing it that they didn't want it to remove it from the game even when they realized it was not good.
This also explains the weird Desmond puzles. Optional sequences in first person that mostly remind me of Portal. They're not specially challenging and the systems of creating blocks to advance don't really fit, not even with the sci-fi plots of the AC world. They're ugly and just reveal some parts of the past of Desmond, nothing interesting. What hurts it's that they replace the optional "tombs" of past games, which were my favorite parts. The main game still has some "tombs" with nifty platform challenges, but being obligatory lack the sense of discovering and adventure.

In conclusion...
I did not hated Assassin's Creed Revelations. It was fun enough. But I can't stop feeling like a rushed sequel. Constantinopla looks great, the animations of the characters are amazing and it has a few cool missions (I LOVED the minstrel quest were you had to disguise as a singer to stop an assasination attempt). But that's not enought. The new systems are bad or lacking, the story is not that good and it plays just too similar to the previous one.
I would like to see a better goodbye to Ezio.