There are two big open world games in development at the moment, Prototype and Infamouse. Ptototype is about a quarentined city and a genetically altered guy who runs around a city absorbing people. Infamouse is about a quarentined city where an event happens that gives some poeple super powers and a guy who has the power to control electricity.
Prototype looks quite forgettable with a main character who absorbs bullets like a fridge, but Infamous really interests me because of the way people you fight have unique powers like teleportation or the ability to control mass. From what I have seen this could lead to some very interesting narrative situations. Unfortunately I will not be playing Infamous because it is PS3 exclusive, and I have no intention of buying a PS3 at it's current price point (as a matter of sanity).
[PS3 Blog via Evil Avatar]