I'm hoping this game achieves the 'perfect mix' of AC1 and AC2 (et al) gameplay.
AC had more open mission design, but nothing to do outside those missions. You could choose however you wanted to approach the actual assassinations and complete them any number of ways, but you always had to do the same sequence of events before-hand and after-wards.
AC2 made the missions much more scripted and linear, and the rest of the games followed suit. The assassinations were much less interesting and multifaceted, but on the plus side, you had a lot of extra stuff to do around the missions.
Give me the big, free-form missions of the first game with all the gameplay enhancements and extra activities of the second game, and you'll probably have one of the best action/adventure games of this generation.