Almost, but not quite the promised land.
The main issue is repetition. Each assassination revolves around the climbing tall buildings/interrogation/pickpocketing triad before you can take on the main target. The strictures of these requirements means that the game, far from being some kind of sandbox experience, feels very much like it is running on rails.
This main gripe is only added to by the flimsy rendering of the NPCs in the game. They may look fantastic and convincing in demos but when playing you can quickly spot the routines each character types runs (the woman holding the pot, the guy that keeps rubbing his hand over his face, etc)They feel like window dressing, and never really integral to the Altair's quests.
Overall, this is a game that will be worth purchasing when it comes down in price. It will give great pleasure over the course of a two or three night rental. just don't expect the pomised land.