One thing brotherhood (PC) has over II (PC) is that it doesn't have retarded LoDs. You can notice the difference very clearly in the cristina missions. This makes the game's cityscape look so much better. On the other hand Rome isn't as interesting as the cities you visit in II. And you don't get to see the impressive interiors until much later on.
Hmmm, this game is pound for pound better than II, a fantastic expansion, but there are some things about it which are just silly. They really don't want to make good combat it seems. In AC1 combat was utterly pointless, in AC2 it got more complex but remained very easy, and in ACB they give you plenty of "win" buttons. Though in ACB's favor, I noticed grabs being more common. Not that it means anything outside the stupid VR missions. The whole process of building up your assassins and the contracts are very boring too.
Going for 100% sync goes a long way and I think the game would have been very boring without it. However they didn't push it enough. To get 100%(or optionally higher) they should have let you stack on rules. A timer, no killing, no detection, no swimming, only kill with x weapon, etc etc. At that point you are dealing with some really good stuff. Sometimes you'd get a rule like no swimming where there is almost no threat of falling into the water, but not so in missions where you are standing all around water. Some missions add a rule in the form that you can't get caught and I'd say these are the best missions in the game. This is why purchasing the Da Vinci DLC is totally worth it. Speaking of which, the Da Vinci warmachines are fucking terrible(worst part of the game), but the part where you are sneaking up to them and destroying the blueprints are really fun.
So if I had a wishlist of what I want to see in the next Assassin's Creed: (Could come in a form of a "hard mode")
-Stack challenges to get 100%(or higher, for fun) sync. Have two to three rules created in place for that challenge to get 100%, then allow players to add universals like timed, no kill, hide bodies, etc.
-Medicine very slowly regenerates health. Maybe stops bleeding/damaged limbs(new mechanic). Have to rely on doctors to get fully healed. (Doctors were pointless in ACB)
-Allow enemies to break weapons if you block too much and do more damage, especially gun fire.
-When overnumbered(4+ to 1), enemies will try to overpowered the player with nonstop attacks(no kung-fu movie stuff), giving you no time to defend. Force the player to either flee or find an way to limit his opponents attacks through terrain. Hell, maybe give them executions if you are sloppy enough and the odds are bad.
-Counters needed to be nerfed in someway. No idea how, maybe require more input or be more situational. As they are now, they make things too easy, especially with the instant kill chains.
-Instant kill chains not a bad idea entirely, since they speed up combat, but they definitely need to have some sort of cost or something.
-As for the third win button, assassins should face limitations similar to(or greater than) mercenaries and etc. It would be awesome if you had to plan out where they could come in advance, mainly for the main story missions, but w/e.
-Lower the amount of ammo you can find on enemies. Makes other sources pointless.
-No more fixed camera angles in lairs/tombs/etc. (Most rage inducing thing about this game, maybe second to driving the tank. It is very, very bad in one of the DLC lairs. The one where you chase that papal guard through the mine or w/e)
EDIT: Oh, this game made Cesare a total bitch, which sucks.