It's kind of a mixed bag. In order to understand the modern day story you do need to be following since the first game but for the past segments you dont!
Ubisoft even goes one step further with the Fate of Atlantis DLC and makes it so that you actually need to read the comics to fully understand some of the characters, which sucks.
Brother anything to do with Ubisoft sucks. Sad but true, that's all!