Assassin's Creed was one of those conflicting games. It had great core mechanics but was pretty weak on the content. Having to complete it nine times to complete it once, I wasn't too excited about the sequel.
But as the release drew close I thought what the heck, I have the money.
But daymn, Assassin's Creed 2 makes the first game look like a tech demo. Pretty much everything has been expanded on, improved and fixed. What a good sequel should be.

The story picks off right at the end of the first game. Templars are angry, assassins are screwed, Desmond runs off to the next--oh does anyone really give a fuck about the frame story here, the guy plugs into another memory-toy and the actual game happens in 15th century Italy. Ezio Auditore is the hero of the day, gets mixed up in the conspiracy, stabbing ensues.

Ok, first off, the repetitive structure has been fixed, the fetch-quests are no longer mandatory. The story flows like in your typical sandbox-game, you're free to rush from story mission to next if you feel like it.
Out of the new mechanics among the more noticeable is the notoriety system. When you do bad things the guards start paying more attention to you. Killing city officials, bribing witnesses and tearing down wanted posters will lower your notoriety.
More aggressive kill moves still increase notoriety regardless of witnesses. I suppose it's a balance issue, as just running up to a guard blade first is quite easy. While it still is easy as pie to remain incognito, the system does give an illusion of long-term causality.

Crowd stealth works right this time around. Well, occationally. In Creed 1 if the guards were to notice you, it didn't matter if there were people or not. Now you can blend into any crowd, no contextual actions or anything, you can even lose chasing guards if you manage to slip into a crowd.
Though, the mechanic is a fickle mistress at best. Even larger crowds are composed of numerous smaller people-clusters, and a few times I found myself without cover in the middle of a crowd. Chalk it down to piss-poor luck but it seemed that the more I needed the cover, the more likely I was to be squeezed out like a ping pong ball from.. well.. the system could have used more work.
Also, the guards are no longer telepathic. When an alert hits, every guard in the city is not immediately on to you. You can even escape guards just by, y'know, escaping from them. When they lose line of sight, they will search the area around your last known position and give up if you're no longer there. But your notoriety goes up.

But play mechanics were the least of the problems Assassin's Creed had. It's the variety in mission design that really earns Creed 2 the extra points. Sure there are your standard races and fetch quests, which are full of shit no matter how good the gameplay. But then there are the missions where you trail targets through the crowds, and as my personal favorite, the assassinations where you first have to locate the target after which how to kill the poor sod is up to you.
Then there are the tombs you have to raid. (see what I did there!) Assassin's Creed 1 perfected 3D-platforming, and now there's some good ole traditional 3D-platforming to do.
And finally there are optional puzzles advancing the big story behind the Templar conspiracy, that got me completely off-guard by not being blatantly obvious. They ask for a keen eye, some logical deduction, pattern recognition, and in one curious case apparently basic knowledge of alternating current. The kind of puzzles I would have expected from Sherlock Holmes vs Alex Mercer, not from a AAA-release aimed for random gamers.

Alongside stabbing dudes and falling off rooftops, you also pimp up the family villa. Starting as a depressing dump, the villa eventually transforms into luxurious mansion where collectible items, weapons, armors and such are displayed. Because nothing says "subtlety" like an enormous mansion covered with assassin banners.
You also buy classical art for the villa, and the game has a short description of every available work. So, in addition of being an awesome game, Creed 2 also teaches you a tiny bit of art history.
But there's one problem. Classical art means tits, but back then people liked fat girls, so the full frontal nudity suffers a quivering and flabby, if strangely soft, hit.
Ezio's appearance is also customizable with different armor sets, dyed clothes and a selection of weapons.

Assassin's Creed being Assassin's Creed, no matter the freedom given, the game still wants you to make a mess of things. Back when the first game came out, I bitched about how it had as much to do with assassins as Kane and Lynch did. As it turns out, I was right in a way. A brief history lesson clued me in on the fact that "assassins" back then were what we call "terrorists" nowdays. The only reason they didn't use bomb vests was the lack of technology.
Case in point. In one mission I carefully slipped past every guard, and as I was preparing to strike the target down without anyone noticing, the game switched to a cinematic where all the guards were dead and Ezio was running screaming towards the target.
Creed 2 still does allow a fuckton more subtle approach most of the time, but will absolutely hate you for it. Really, I have never seen a game disk that bitter.
Also, in some missions the freedom is fucked sideways as the game drops into completely scripted tube. Fortunately those were strictly in the minority but such hoops are especially irritating when they're presented next to the freedom of most of the game.

The fighting, when you're forced into it, works quite well. Basics are the same as in the first game, but control and feedback have been patched. Out of the new tricks among the more useful was the disarming move, which is only available if unarmed. So strangely enough, the safest way to deal with bigger enemies is to go against them with bare hands. It's possible to lose your own weapon if knocked down, and enemies can continue fighting disarmed, unless their morale fails and they decide to bolt.
As a nifty visual detail, even when you hit an enemy, you don't cut them with the blade. The health of the enemies is represented as kind of stamina, and when they tire you get through their guard.
Gives the combat more realistic look as you're not stabbing them in the gut with every hit.
(did the first Creed do this? I can't remember)

I've yet to complete the game, at the time of writing this I'm nine chapters in and playtime is clocking at 20 hours, so I'm pretty much ready to state my approval here.
Some irritating missions and occational hiccups aside, Assassin's Creed 2 is a game I'd almost dare to recommend for most people with functional thumbs, it's that good. Even those who hated the first game.
I didn't have high hopes for the sequel, but being wrong rarely feels this good.