AC as a series is fine, I don't think innovation for the sake of innovation is a good idea. Fans seem to be rather happy with the way the series has been going which is why people still line up to buy them. That said the current AC game did wind up majorly burning PC gamers who pre-ordered by going on sale for 40% off a few weeks after release via a STEAM sale. The theme of that sale was award winning games or something like that. I put up a complaint to STEAM about that one in their forums since I had just bought the game for full price, not that they seemed to care.
See, I'm one of those people who sits down and believes if something works there is no reason to fix it. I don't like how a lot of series like say "Mass Effect" morphed into something very different than what they started as despite claims that it's all the same thing. At least the AC series comes with a specific expectation of what kind of game it is and how it's going to play and be balanced and manages to fulfill that.
I personally would like to see Ubisoft experiment a bit, but that means launching new IPs to do it right, and their last attempt to change things up a bit "Watch Dogs" was a bit of a failure.
That said I will admit I haven't been a big AC fan until fairly recently, it was "Black Flag" that convinced me to give them a shot and I had a lot of fun with it. I went back and tried AC III and it was "meh", Unity was okay though as I liked the place and period. "Rogue" is okay but I haven't finished it yet, it seems to be trying to blend III and IV with mixed results that and I think it was trying a bit too hard with the whole "air rifle and grenade launcher" additions. "Syndicate" is okay, but the big problem I have with it is the whole way the game is leveled, I'm an RPG fan, but this isn't an RPG or action RPG series, gear in assassin's creed should not have a 'you must be this cool to equip' specification and the whole idea seems to be to force me to explore the city and clear things out in a specific order as opposed to being able to proceed in any direction I like. What's more the general mechanic of clearing viewpoints and then seeing everything that is around seems to be gone and largely replaced by "grind for money, or have your gang bring it in, and then buy a treasure map for each type of thing to be found" which to me seems to be a way of padding out the time things are supposed to take.
AC had a really buggy game that was decent once it worked in "Unity" and what feels like a mess to me in "Syndicate" which I haven't been playing that much. A couple of bad installments in a series like this isn't anything to get concerned about, especially seeing as AC's failures are arguably still more successful than the victories by a lot of the competition. Of course Ubisoft's business practices are still horrible, I mean letting STEAM put the game down for 40% off that quickly was low, and the sad thing is that they seemed to be screwing all of the loyal customers in the process of doing a victory lap over how well the game performed.
I'm really surprised there hasn't been more expressed outrage over that sale/price cut.