So I've been playing this on my days off and it has been a blast. I had lots of fun with AC2 and this is mainly the same thing but it's got considerally more cool stuff attached to it. Some of it may not be super deep but just roaming around the streets of Rome and thinking, what should I do now? And the list of things to do goes on and on, your always running into stuff you can buy, side quests to take on, treasure to hunt, etc. Plus having your own group of Assassins to deploy death on just about anything never gets old. Oh and one of the best parts, you can now buy maps for the flag and feather locations, woot!
If you enjoyed the AC games at all this is a must buy, also if you were turned off by the first AC game, do check out 2. In fact I highly recommend playing through it before going into Brotherhood since it literally picks up exactly where 2 leaves off.
Oh and one more bit of advice, the items you get off treasure chests and thieves, do not sell them, keep them, you'll need them for the merchant quests. Made the mistake of selling off a bunch of it in the beginning and since there's no manual (thanks Ubisoft) I had no idea what they were for.