As you increase in level, your options expand. For example, when you obtain your ship (there is no specific level at which you obtain the ship), you can travel to different planets such as Nar Shaddaa, Tatooine, Alderaan, Hoth, etc.
The amount of planets are limited, however, with the amount of potential this game has, I wouldn't be surprised to see many, many more planets and worlds included in future expansion packs.
There is a lot to do; trust me. I am level 21, and I am still finding things to do.. it's a little overwhelming, actually.
Oh, and did I mention that you can use your ship to engage in space dog-fights for a lot of EXP?