Ok, folks, it's hit the shelves, I know some of you bought it. Against my better judgment so did I (not because I didn't think I'd like it, quite the contrary, I have 5 papers due over the next few weeks.)
So What are people's thought's thusfar. Remember thy spoiler tags as well.

I think this is a significant improvement over the original game, while still maintaining the core elements that made it fun. I like that blending is now something you can do with everyone (rather than just monks) as a trade off though, it's no longer automatic (Hold A, wait until you're where you want to go, then let go) rather you have to maintain pace with the group. The addition of purchasble "factions" (or groups that follow and distract others) is a bit of fun too. Nothing lights up my play time more than sending a bounch of "courtisans" over to some gaurds then sneaking around them. My one complaint about this is that it's almost too well integerated. At times it's basically required to do something of this sort, and other options I try aren't nearly as successful.
Assassinations have been greatly improved. I'm not too far into the main plot yet, so I haven't done anything that qualifies as an "assassination" yet, rather open killings that for plot reasons you don't hide from. I'm told it gets different though once the main plot moves along. (I have assassinated guards and side characters though, using the new stealth moves.)
I love that even when your notorius gaurds still take time to notice you, rather than the old style "THERE HE IS" every time one even so much appeared on the screen. This gives you time to actually be stealthy, and avoid confrontation.

Con Note: The "economy" in the new game seems a bit tacked on. It's like they wanted to do something cool, then just kinda forgot. So rather than make you solely relying on the money making missions (like courier runs and the like) (possible spoiler regarding economy workings?) you have a villa which makes you money as well, fable style every 20 minutes. Also you get money after each mission is complete. Finally there is an absurd and disbelief breaking number of chests with gold in them around END
Nevertheless, I really really enjoy the game. And it's hard to pull myself away for paper writing. I think it was Joystiq that say "This makes it look like the first game was a proof of concept" and it's right in some ways, (I still liked the old AC alot, I just like this one more.)

One final note on collectables. Unlike the old game, in which they made absolutely no sense as in they were merely tacked on and served no reason to actually collect them short of achievements and completionism, the collectables are well integrated this time. Most/all of them have some plot tie in, and while they all may not reveal major plot lines, at least they aren't just randomly there (I'm looking at you templar flags from AC 1).

It looks a lot better than the first one, but I probably won't pick it up until after Christmas.

Also, somebody in my class was talking about the puzzles being hard. Insert stereotypical college athlete as that somebody, so what is the difficulty of the puzzles like? If you've run into any. I'm guessing it's no Layton, but compared to Prince of Persia...?

It actually compares a lot to the PoP series. Ubisoft does a few things well, Stealth, Puzzle, and action figher. As I was playing last night, I thought "Man this is like PoP meets Splinter Cell". Not that that's a bad thing. The story is unique enough, and the differences great enough, that it's all good.
Puzzle's I've reached so far have typically been of "meh" difficulty, usually just figuring out where to Pakour and accomplishing said goal. Perhaps though they'll get harder.

That being said:
I had a switch I couldn't find for like 20 minutes. It was right out in the open though, and glowing, so I think that was a case of "forest for the trees" syndrome.

The collections can be a bit hard. It tells you where the Codex Pages are (after you use the view point) and you can buy maps for the treasures but Feathers, statues, glyphs and the like (The latter being main plot line important) vary from "No help at all" (besides glitter when you get close) to "We'll tell you it's somewhere in/on this building, but that's it" and that can get pretty tough.

The way they talked about the puzzles, it sounded like "Here's a hint, here's some pictures of stuff, get to it"

Oh, the Glyph Puzzles. Yeah those are strange. There are only 20 of them, and there are actually 6 different types. They can get a bit pixelbitchy at times, but eventually the game give you a pretty heafty nudge.

I just picked up AC2 by surprise myself and while I like the visual change and aesthetics, what's-his-face doesn't come off as a strong character when put next to Altair. On top of that, the traditional problems with controls return. While free-running, I find myself often getting punted off to the side of where I want to go, or "fall hard" against buildings if the angle isn't right.