This is a flat-out, great game.
This sequel fixes all the first game's problems and adds more to it, in new, unique ways.
The story continues directly after the first one, and you play as a new character, Ezio. You will get to know him better than you did Altair (although he himself was a very interesting character), and even then you get some character development from Altair as well.
As the story unfolds, you get to know your city and Ezio's family. And unlike the first one, they give you some determination and a reason to complete the game. There is a driving force behind Ezio's actions and you are compelled to stay and play through the game.
You even pick up a few new tricks along the way, such as wall jumping and climb leaping. As you should know, Leonardo (the brilliant artist and inventor of course) supplies you with new weapons as you progress and is your constant ally. It is a tad sad that he isn't that important as a character in the plot asides from giving you encouraging support and some new assassination techniques (which other characters could have done). But it's still nice to see his smiling self during your grim missions.
The story telling is a bit confusing, as Ezio and some of the other characters talk and you have to uncover the plot from their dialogue. You could be doing your own thing, next thing you know, you're in the middle of a climatic point in the game. In my case, I was a little puzzled at the mention of The Vault, since I was not paying close attention to their conversations and hardly remember them mentioning it.
That said, there are no cutscenes. But I prefer it that way. It's all interactive and the only time you aren't in control is when the story is being told and when someone wants to say some witty dialogue (the game's dialogue isn't that good, but it's not bad).
The controls are very tight and fluid, allowing you to gracefully run on rooftops and such (considering you're actually pushing the stick in the direction you want to go *glares at certain reviews*). But they are VERY tight, and if you aren't specific with your directions, you can end up falling to your death. But that shouldn't be a problem.
There are Assassin Tombs that test such skills and they are cleverly laid out. Ezio rarely ever feels stiff and runs fluidly and feels very agile, as he should.
This game is also very cinematic and dynamic, putting you in some very dire situations. One such sequence has you riding a carriage being chased by enemies riding on horse back. Another has you flying through the air on one of Leonardo's inventions. It goes on.
The missions are MUCH more varied than the first one, making it infinitely better and funner than the first one. Also, each mission lets you tackle it however way you like. You can run in and fight off a swarm of guards, or play it stealthy. They give you so much freedom in how to do things, and choices are always nice.
The combat itself is improved. Countering is still king, allowing you to kill nearly any enemy in a single counter. And while easy at first, the combat becomes increasingly difficult, as countering won't always work and button mashing won't get you too far, as you are bound to be struck from behind or when facing a brute warrior, they'll take your hits like nothing and will pummel you into a pulp unless you use some of your other, lesser known skills, such as dodge and strafe. The difficulty only gets hard to a certain point however, and you can still manage with button mash, counter, dodge, and disarm, which takes away some of the joy from one-on-one combat, as it is ridiculously easy.
The sequences as Desmond aren't as thrilling as Ezio's, but it's still fun, unique, and interesting. He can do much more now than the first game, and continues to become increasingly skilled as you progress, which makes you want to play him more often, as modern day assassins are nifty, no?
The cities and environments are all loud and bustling with life. They are varied, from a poor town, to a swampy outpost, to a living city. And you will especially notice that Venice kind of stands out, and is where you will spend a good portion of the game. You can manually travel to each location and enjoy the view, or you can quick-travel to each city.
You yourself get your own Villa, and can manage it. It starts as a deserted town and eventually people will come by as you improve upon it. The game has its own economy system, and while assassinations give you lots of money, the Villa is your main source of income.
With money, you can buy better weapons, restock on supplies, buy new colors for your robes, improve your city, and so on. Money. Useful stuff.
On a side note, your health doesn't recover by itself anymore. You need to buy medicine from the doctor, but it's not much of a hassle.
There is an object called the Codex, which you will need to finish the game. It's a book that's been ripped to pieces. As you collect the pages, you can decode them from Leonardo, and through there, you can get some insight on Altair, as it was his journal. Not bad huh?
The game has some minor plot twists that don't affect anything too much, but it takes an HUGE turn at the end. It's creepy ending might confuse you, but it only adds to the story's depth and isn't a bad thing if the third is done right.
Once you are done, or have some spare time, you can collect feathers and/or glyphs that you see. Feathers unlock a couple of items and finding and then solving glyphs unlock a video called "The Truth." And Al Gore has nothing to do with it. I do find it disappointing that this and the Assassin's Tombs are the only source of replay value, if they can be called that, considering you can collect them all in one playthrough (although it will take an ample amount of time). Alternative costumes, extra weapons, replayability of chapters, or even a "New Game +" would have been appreciated.
The game has a bonus feature with U-Play, where if you have online connection, you can earn points by progressing through the game and unlock special items, such as an Altair skin. Or you can sync it with Assassin's Creed: Bloodlines and obtain special weapons. And that's all neat.
There are two portions of the game that is notably missing. Those will be DLC in January and February of 2010. Look out for that. Should cost roughly $10 total for them both. Which isn't a steep price.
This game has tons of life, features, variety, missions, personality, and such that it's hard to pass up on this game. Assassin's Creed II is fantastic and leaves you wanting more.