I don't want any spoilers, but from what I've seen, there really aren't that many locations in DOS, at least not as many as in BG2. I spent months playing BG2, doing every single quest, picking up every single item. I really hope DOS is a lot like that, but some say there are only 2 big towns where you can sell your items, one of which is Cyseal...
I was hoping for snowy mountains, dry deserts, humid swamps, bushy forests, underground caverns, underwater dwellings, and of course inter-dimensional existences / space.
In trailers I saw mostly Cyseal-like environments along with snowy ones and some underground-like ones, but that is it... even Dragon Ages: Origins was bigger than that!
Anyway, I wish someone would post 1 screenshot from each different environment in the game, so I can assess its size that way!