There are signs when these civilizations come to an end
I like the series. I've played & completed the first game and ACII. I have Brotherhood, but I dropped it because I felt like since Revelations came out, they've just been milking it for all it's worth.
However, I got ACIII for christmas and I'm currently playing it and enjoying it so far, even though I had to fill in the gaps of the story of the other two in between games with Assassin's Creed Wiki
My favorite in the series is without a doubt ACII. Ezio was just so much more likable a character than Altaiir, not too mention it was far less repetitive than ACI (which was still a fun game, just repetitive to a noticeable degree). Altaiir was just some generic dude, whereas Ezio had a real roguish charm behind him that made him just so lovable, kind of like Han Solo.
I haven't gotten to the point of ACIII where I'm playing Connor or whatever his name is, so you'll have to wait for my analysis of him.