This game is a definite improvement on its predecessor. The controls are obviously a lot more refined and the new missions etc are an interesting part of the game.
Ezio is, honestly, so much better at being an Assassin than Altair was- which is odd, because Altair had been trained in Assassination, jumping and the other ways of the Assassin whereas Ezio was just pro at climbing buildings (one of many hobbies he enjoyed in his hometown).
This game is full of new, exciting things to do! You can actually have money this time; allowing you to buy armor, paintings, medicine, poison and more. You can increase the amount of money you have by stealing, finding treasure, completing quests or improving an area in the game (this area also gives you an income, which is pretty cool).
As well as money, this game has a new character- Ezio. Although the way he controls is more down to refinement by the developers, I still find him a much more likeable character than Altair. He's cocky, but not in such a way that makes you smile a little inside whenever he nearly dies. Ezio has a nicely developed backstory that makes you genuinely feel sorry for him when bad things happen, and happy for him when the opposite occurs.
The quests, too, are very different in this game. As well the "kill these dudes because they're our enemies" plot, you can get Glyphs (these reveal "The Truth", which is confusing as anything) and also Codex Pages (they make a map thing). To get Glyphs, you have to search specific areas- some of these areas aren't available at first, so you have to unlock them. Getting Codex pages is perhaps one of my favourite things to do in this game, as you can use courtesans to distract the guards- which I find amusing!
The graphics are my favourite change in this game, as everything is so much prettier. Perhaps the first game was so grey because the first Animus was glitchy? But the reason doesn't matter, the game has colour and vibrancy and this is one of the elements that really sets it apart from Assassin's Creed.
But the old things still work
This game also contains callbacks to its predecessor. View Points, for example, still reveal bits of the world to you. Your quest to kill Templars continues, but your weapons are much cooler than previously- as is the way you can use them.
Parkour is, again, a pretty important element in the game. And Ezio is so good at it! You can grab high up ledges, go round corners and even swim (which is kind of a necessity, as some of the game is set in Venice).
I really enjoyed this game. The team behind it really seem to have improved upon the first game, and in all of the right ways. Even if you haven't played Assassin's Creed, I'd suggest you give it a go.