In liberating Rome from the Borgia, Ezio systematically took over districts throughout the city by assassinating Borgia captains. Revelations builds upon this idea further with great success replacing the Borgia with Templars in this Ottoman setting. Once again, Ezio can liberate small areas by taking out the respective district's captain. Yet there's an added level of complexity as a greater effort is needed to keep this territory.
The power struggle between the Assassins and the Templars also plays out in the series' newly added tower defense mode. With Ezio overseeing these sieges from a rooftop, he places barricades in the path of the invading Templars and assigns units to spots along the sides of the path or behind the barricades.
It always feels like you have a chance as prevailing; it's just a matter of multitasking well enough to have effective units in the field. The selection of troops are well-suited to this kind of gameplay, with archers, riflemen, and air assassins to choose from, all of whom have their strengths and weaknesses. Ezio's usefulness beyond placing units extends to the ability to shoot enemies and call in a cannon airstrike.
One of my favorite features of last year's Assassin's Creed: Brotherhood was the ability to enlist noble citizens to join your ranks. This returns in Revelations where you're once again able to send out assassins throughout the Mediterranean to liberate those regions from Templar influence. Whoever isn't off on a mission are readily available to help Ezio with his own goals in Constantinople, mostly to help clear out rooftop Templars or help you even the odds during a sword fight.
What has always sold me on Ezio's arc in the series are the linear exploration sections which have been designed as a change of pace from the sandbox gameplay. In Assassin's Creed II it was the engrossing platforming in the churches. In Brotherhood it was the Romulus Lairs. Revelations finds Ezio exploring the underground depths of Constantinople as he races against the Templars in finding the Masyaf keys.
It's a spoiler in itself to delve into how these sections play out, but I can at least say that there's variety to look forward to, not to mention platforming sections that would make Nathan Drake blush.