Entire series is flawed
Ubisoft managed to shoot themselves in the foot with the very first title. Contrary to popular belief you're never playing an assassin in these games. No, you're playing a dork from the future called Desmond (or in later titles, another dork) who is playing an assassin. A simulation of a simulation of an assassin. The game would have been more interesting if the player dropped straight into the story with all the animus / future shit just cut straight out. Reveal the story through actions of the protagonist / antagonist and allow the lore to build up slowly.
Aside from that AC titles are just too repetitive. They're also the same thing over and over. Other sandbox titles, particularly Rockstar ones recognize how boring a world is if you're doing the same stuff over and over. So they pack in an insane amount of diversions and silliness to keep the game engaging. Not so with AC which cut and pastes the same content all over the map. Ubisoft do this a lot with Far Cry and Watchdogs suffering the same issue.