I have to agree with Yahtzee; you spend so much time out at sea, you really don't want to go on land for more than a few minutes. It did get a bit tedious that many other ships were more overpowered than you were early on, but all-in-all, I liked the whole sailing business. Will it work for new games? Eh...maybe?
That line graph was a pretty epic explanation for the series as a whole though. The way that the series presents the conflict of the Templars and the Assassins is a philosophical one, and a conflict that can't be solved. Period. Because of that, Ubisoft will never be able to create a believable "happily ever after" ending. The present day stuff will just end with a temporary victory for one side, before the other gains the upper hand again. Its like the Templars say "The only requirement for the Templars to exist is that the world be what it is."
Don't get me wrong though, I still love the series, and I hope that it can adequately continue to present new time frames for us to explore, and HOPEFULLY solve the whole present day stuff.