In a nutshell, this (so far) looks like the game that Assassin's Creed wanted to be.
So, a confession. I never finished the first game. Made it maybe 2⁄3 of the way through, dropped the game for a few months, restarted from scratch and made it through the first mission, and then just quit on the game. While an interesting setting/idea, the basic gameplay went
- climb towers to reveal map of the city
- pickpocket mission (x2)
- The Big Kill
Along the way, several optional missions to help out citizens in distress and quests to find various collections of items rounded things out. Unfortunately, this same formula was repeated in all 9 missions of the game, meaning that after the third quest (or thereabouts) things rapidly turned into a tedious, repetitive slog and the desire to finish the game quickly evaporated. Even in the side quests for the various flags, spending hours hunting through a section of the city for that one last flag or two (that had no actual bearing on the game at all) made the eyes bleed, and I can only imagine the hatred and rage felt by people that had 90 or more out of 100 of the things, and had to try and backtrack through the cities and lands to try and figure out which ones they had gotten and which ones that they were missing were.
Fortunately, Assassin's Creed II seems to have fixed most of these flaws. The basic flow has moved from hitting the marked spots on the map to get the Plot Tokens to go forward and centers now around interacting with characters and getting tasks from them to advance the plot (much in the same vein as Mass Effect), most of which end up breaking down into several smaller tasks. The various side quests now are for the most part things that are identified on the maps and have actual use and bearing in the game, making it worthwhile to make the effort to complete them. The "Eagle Vision" ability is now useful in helping to find hidden items of interest (like unmarked side quest items), and notoriety is something that can go up and down based on your actions (instead of being constantly "on" in the first game). Fighting has even gotten some major attention, with several different types of enemies (with different weapons and modes of attack), all of whom don't fall for the "turn a corner and dive into a pile of hay to suddenly turn invisible" trick.
To be sure, there are some drawbacks. The need to periodically head back to the Villa to empty out the tax chest after it fills up tends to break up the game flow (and having to backtrack across an entire city to get to the one exit is not all that fun), and between that and all of the side quests it tends to get in the way of the main story line a bit and make things feel a bit cramped, but after having played for a couple of evenings I'm still interested in playing the game, as opposed to just going to Wikipedia to read the plot synopsis and skipping the game entirely.
All in all, not a bad way to spend the time between now and when Mass Effect 2 comes out.