Blighthaven is a landscape dominated by the Strain's mutated minions along with uncontrolled Eldan machinery, featuring such comfortable-sounding regions as the Cankertube Swamps, the Globellum, the Sanctuary of the Keepers, and the Genesis Chamber. It's prime territory for new content to explore what happened to the Eldan as well as understand the virulent opponent that is the Strain.
The Northern Wastes, meanwhile, brings players back to the Northern Wilds after the events in the early game, with both Dominion and Exiles struggling to claim the territory... until a new threat emerges from the Eldan bio-labs in the area. New events, challenges, missions, and path content awaits players in the zone. It's all adding up to plenty of content for a first update; you can check out the official reveal page for a few extra details.
[Source: Carbine Studios press release]