Perhaps a good way to speculate about the film would be to view the 'ultimate' trailer compilations.
[youtube]https://www.youtube.com/watch?v=tUswgEuRgVY[/youtube]
I counted three distinct environments in the trailers.. Tatooine, a lush green planet that might at least be derived the location of the rebel base on Yavin 4 from A New Hope, and a snowy but forested planet. Considering some scenes of X-Wings engaging the remnant [?] forces on the forested planet one thinks it may not be Yavin but some other place like Kashyyyk, the Wookie homeworld...
I think this bodes a bit well, seems like they're not overextending themselves. Time spent in space seems to be kept to a minimum if the trailers are anything to go by, but we see the key characters engaging in wordless moments in at least the first two locations, which suggests the presence of a story...
Hmm!
BTW I detest Von Sydow's "...and the light" narration of the advert, I mean how dry and crackly can you make your voice buddy?
Also, I can only assume the new Sith has no idea what really happened to Vader, and as such is some kind of neo-Sith, a la Neo-Nazis, which might not be the most interesting backstory.