I just started playing the first game last month. (Don't worry about spoilers, I know most of the plot for all the games.) I wish they had left out the modern portions, though I'd be infracted if I embellished on that beyond my belief that the Assassins would not support the people that the Québécoise support these days. But the historic portrayal of the Crusades so far is pretty spot on, and I'm loving a lot of the internal conflict Altäir is having over the creed and the purpose of the assassins. Themes of duality and self sacrifice always jive pretty good with me. No complaints about the combat system here, because I feel like it was built for people like me who have terrible hand eye coordination and can't play normal games.
After accidentally watching Embers, I want at least a Vita game following the Chinese assassin guild. I know everyone else wants Japan, but everybody knows about how ninjas work. We don't know as much about Chinese history, and there is a very rich set of weapons and martial arts to pull from. I'm imaging Shaolin spades and meteor hammers.