I just finished, and it's a definite WTF ending.
Overall, very good game. They added enough extra collectibles and missions to keep you interested throughout the game. The main story starts off slow but by the last few sequences I couldn't put the controller down...even though I had no idea what was going on with the story.
Some complaints...the assassination sequences (boss battles) were horribly flat and anti-climactic. In AC1 these sequences took place at a big gathering or event and made it feels as if there was some risk involved in moving throughout the area, also the gaurds pursued much better in AC1. In AC2 run up one building and you are home free after you just killed some major figure in history.
I'd like to see the next game up the difficulty overall, or if nothing else for the assassination sequences. I'd also like to see some destructable environments that you could use against your enemies. There were so many times when you are perched above enemies where it would be cool if there were a way to drop or collapse something on top of them and escape without ever being seen.
Now, it's time to try and 100% this beast. I've never fully completed a game and this is the first one i feel like it wouldn't be utter torture to go through again and find all the collectibles.