Yea, you need to start at the beginning to get the very most out of the series, or at least Assassins Creed 2 to get all of Ezio's story (good to play 1 to know who Altiar is and to thoroughly enjoy the ending of Revelations though, imo). Game play is a lot of fun! Story with the Assassins is good, but a tad corny (the ending - not going to give it away). Story with the animus and everything involving Desmond (and today's time), ESP the add on puzzle things in Revelations, I think, is really stupid. But you need something to tie all the assassin's creed games together, and the idea in itself is interesting but I hate Desmond so that aids in it being a real turn off in that dimension for me. Altair and Ezio are great though! plus that's the main focal point of the games anyhow, so it's good; love the assassins.
-The franchise has recently been facing court battles due to story infringement; the author of the book "LINK" claims they stole the plot from him. Ive read the details and heard the story comparisons. "LINK" sounds like a more interesting reworking of the modern aspects (with Desmond), if you like that part of the game/story. Just thought I'd throw that out there since we're on the topic of assassin's creed.