At least there is a year Gap, So I'll be able to forget about the gameplay staying exactly the same through out the series, nothing has changed except for the story line, and I have to be honest, Its starting to get really boring.
Uhmmm what the hell are you expecting .-.?
I mean sure the basis gameplay has remained the same, but that is because it works. They changed the combat mechanics quite a bit over the series. In AC 1 combat was fine, but lacked something, AC 2 that was rectified and it was made more fluid in Brotherhood they added execution streaks, which was at times annoying but rewarding at the same time. In AC 2 the ability to buy and renovate buildings was added and it was continued in AC Brotherhood.
In Brotherhood they added a shop quest system that made you work for those shiny items and pieces of armor (although it was made useless but the armor of Brutus

) They also added conditions under which to get full synchronization.
The arsenal of weapons available to you also evolved. We also see in Brotherhood that you gained the ability to use some environmental weapons to complete missions, plus you got the ability to kill people with a broom ^_^
In Brotherhood we even saw the arrival of MP. I mean sure I haven't tried it because my friends moved on since I got AC Bortherhood so late, and sure it didn't catch on like Battlefield and COD MP games but at least it showed some innovation and what was possible with the franchise.
Now tell me that the series hasn't gone one step better gameplay wise every time? Would you rather sit with a refined combat system, versus a system that changes everytime and still leaves a bitter taste in your mouth? I mean really. You're basically just palming off every single franchise out there with your ignorant statement since all of them have their signature gameplay mechanics they they build upon instead of re-inventing the wheel everytime and watering everything else down. I mean look at the Battlefield series. It builds upon it's previous gameplay successes, COD, Half-Life, GTA and the list goes on. Each franchise has it's own gameplay and with every iteration they build upon the past iterations, because they worked.