I've finally torn myself from the game's delicious multiplayer to sit down and come back to Ezio's story.
I'm hardly into the SP at all, still in sequence 2, but already the game has demonstrated its flaws and strengths vs. AC2, IMO. For one, the collectibles are inexplicable (I get why I'm tearing down Borgia flags, but why am I collecting feathers again? Maybe this will be explained a bit later...) BUT they are far superior in design. Rather than being an annoyance of standing on every rooftop and looking very closely with eagle vision, when you're in eyesight, they appear on your map. Instead, however, the difficulty has changed such that most of them have become mini-platforming puzzles unto themselves, which is far more rewarding to figure out.
The expansion of the villa's upgrade system for money to encompassing all of Rome is, I think, a bit too tediously large. Way way way too much stuff to purchase, especially when in AC2 your reward, at the end, is to basically make money worthless. Woo. However, the assassinations you have to pull off to unlock shops can be tremendously fun and occasionally put AC2's actual storyline missions to shame. Also, there's something pretty awesome about being able to renovate and own the Colosseum, among other Roman landmarks.
It feels apparent to me that this is a much shorter game than AC2 was already. Fortunately, it's already demonstrated a much more interesting, tighter narrative and the addition of synchronization percentage makes each individual mission far more interesting. You can complete a mission however you wish, but to unlock bonuses and hidden memories, you have to do it exactly how Ezio remembers doing it. Sure, you can shoot your assassination target, but Ezio grabbed that fucker and made a building collapse on him, so you should too. It's optional added difficulty and flavor that's really enjoyable.
I have nothing bad to say about Rome's design, however. It's a much more organic map than any of the AC2 cities and I'm having fun exploring it.
Ultimately, if the bad bits were necessary to obtain the good, it was entirely worth it. I'm having a fucking blast with this.