The map is roughly the same as the first game: a few cities all connected by a large open area (The Frontier).
Liberating cities is much like in Brotherhood: unseat the Redcoats from forts, complete activities, etc.
As far as I know, there isn't a parachute in AC3.
Play time varies. I beat the main story in about three days, but beating all the challenges, naval missions, and side quests can provide for more play time than the main quest.
There are 12 sequences in AC3.