The lights are on
In some ways the series has definitely taken a step or two backwards so I do agree with you in some ways. I think they took some of the new ideas a bit too far more than anything else. I like the idea of the camera moving to give a more epic view of the environment, but the fact that it can't be changed and the frequency with which it occurs drag it down.
The more frustrating change to me was how strong the Janissaries are. For the first time in the series I felt weak. I don't mind a good challenge, but that's crazy. The papal guards in AC:B were overhyped and just plain easy to kill, but the Janissaries went too far. They're fast enough to keep up on the ground, and they just refuse to die. In AC:B the agile guards could catch you sure, but the brutes were slow to compensate for their extra armor. The Janissaries don't really have a weakness. You can't attack, counterkill, grab, or even kick them; you can steal from them, but that doesn't do you any good. The only good ways to kill them involve bombs(overhyped) or throwing knives. And, as if that wasn't enough, they're everywhere!
The changes to the weapons were a mixed bag. The throwing knives haven't been good since the first game, so it was nice to have those back as a functional option, but not at the expense of the crossbow. Shooting anything other than a rooftop guard with that thing is useless. Before the game was released Ubisoft kept pushing the bombs, as a huge new feature, but the only ones I used were smoke bombs. They would be better, but they're awkward to use in combat and it's too easy to kill civilians if you throw them at guards on patrol. It's just plain annoying to get warning messages about killing civilians every time you want to kill a group of guards.
I'm not going to get started about the den defenses because I have nothing new to add to that.
The thing that killed me most was how short the single player was. I don't mind that they added multiplayer in AC:B, but it's starting to take over the series. The story was what made the series huge in the first place and now that's suffering to appeal to the multiplayer crowd.
Now that I'm done complaining, I think there are some huge improvements in AC:R. The hookblade was a lot of fun. It sped up the climbing, and added to combat in interesting ways. The ziplines, though illogical, sped up travel and were just plain fun. Using the hanging pots to longjump was a great way to escape the guards. I also think that Constantinople was most interesting city the series has ever done. Its diversity and architecture made it a joy to explore. Sure Renaissance Italy was gorgeous and majestic, but Constantinople feels more real, maybe because there's more socioeconomic diversity. Yusuf and Sofia were interesting new characters as well. In AC:B it felt like the cast from AC 2 was shoehorned into Rome where they didn't really fit, so it was nice to see new faces. The range of new ways to recruit assassins was a nice change and I also appreciated the fact that you can interact with them a little, it makes you care a bit rather than just seeing them as another weapon.
I don't think the game as a whole sucks, I do think that the development team added some things that no one was asking for; and I believe that single player suffered because of the success of multiplayer, but that issue effects every series that does both.