As far as i've seen, there's both options. Single Player where you have dominion over every planet in the galaxy, create new races and watch them interact and learn from one another, watch them grow and evolve, create technology, eventually become civilizations that generate politics with one another...etc. A sandbox game that only ends when you get bored (or manage to populate or destroy every planet in every solar system in the galaxy, I guess).
On the other hand there's the online phase, which is both co-op and Pvp. Each player gets control of a planet or two, creates their races and begin to help or conquor one another. I suppose eventually if a server was up long enough one player could dominate the whole galaxy, but i'm much more interested in creating my own species and seeing what other people come up withand how they fare with one another (will they talk, trade, or eat each other?).
Seriously, limitless possibilities. Seemingly infinite species creation options, completely freeform non-linear gameplay, spanning a whole galaxy. This is the only game I want right now. Any idea of system specs and/or release date?