What is the most memorable thing in a specific Assassin's Creed city you've played?
The first time you walk out of a Spy Base on the opposite side of the Thames with Churchill in World War 1. The view is absolutely gorgeous; there's that blood red afternoon sky, with incredible smoke effects and airplanes buzzing by, as well as the sea busy with all the warships. I was loving in love from the first sight.
For other, older experiences...
There's also something very satisfying about the way Florence in AC2 was constructed. That first time you climb up onto the rooftops and jump your way around the city without having to rush through the crowds below which you've already been doing for a while.
And despite it's flaws, Assassin's Creed III had some faultless enemy garrison encounters, such as the one on the south-west of the Frontier. There's several entry points including the tree tops, plenty of cover and about 50 guards in isolated positions that allow you to either slowly work your way through or just go blitzkrieg.