When James Cameron's Avatar was released in 2009, it was criticized for having a story similar to Pocahontas. Despite its amazing visual effects and spectacular action, the film's story was clearly unoriginal, but according to Sam Worthington, the sequel will be nothing like we've ever seen before.
During an interview with We Got This Covered, Worthington said:
"They're going to be shooting concurrently. The plan is to have some time in between, I think, but these things are always ambiguous until they start. We're still set to start in the summer, though. James needed time to perfect the scripts. Whenever he says jump I go because he's the man. I've read all the scripts, they're great. This is going to be Jake eight years later, and he's got a family now.
This film is going to be like nothing you've ever seen. The world is bigger than the first one, but essentially, it's a movie about family. Jake will still have that essence of a kid seeing the world for the first time, but he's been living in the world for a while now, so what's this world he's seeing now for the first time? The film will explore that within this family dynamic."
It sounds like Jake Sully and his family (including Zoe Saldana's Neytiri) will explore a new area of Pandora we've never seen in the first film, and considering that it will be shot using underwater technology, we'll probably see them explore the sea.
Cameron announced that there will be four Avatar sequels planned, and the second one is set to release on Decmeber 2018, but production hasn't started yet.