After completing the tutorial and earning your captain's seat, the galaxy pretty much opens up to you. As far as size goes, well, there's a lot of space to explore. Hopefully Cryptic is planning to incorporate support for accessing music from your computer via the game, because space is noticeably vast in STO. I've managed to venture into Klingon and Romulan territory, although it was most certainly beyond my level. To say I died without much fuss would be a kind and generous version of the story.
Most of my missions took place near and on planets, but some occurred within space stations or in unexplored territory. Missions are given out by all sorts of NPCs, but Admirals are a primary source of the story-driven Episode Missions. These are designed to simulate the feel of a Star Trek episode within the game itself and I completed quite a few of them. Most of them last quite some time and consist of several different objectives, although, yes, once in a while I killed X of Y.
After a while, however, I started to take on missions to explore unknown space. One thing I especially liked about grabbing missions was that you could do it from the comfort of your ship by contacting Starfleet. I also ran into some straight up diplomatic missions. One mission in particular had me resolving disputes on a Federation mining colony. These missions hold a lot of potential and if Cryptic continues to evolve and expand upon what can be done here, they'll have something that very few other MMOs possess: a way to regularly feel heroic without shooting or hitting something or someone.
The subject of PvP has been covered pretty well, although for Federation players it's merely another way to level up as opposed to the primary method on the Klingon side. Still, flying through space with other Federation players filled me with a potent degree of Star Trek nerd glee.
Fleet Actions also aim to make players feel as if they're right smack in the middle of an episode or movie from the series. These are all about big battles between huge forces, whether they be Klingon, Borg or basically any kind of space menace. You can grab a mission to do them, or you can just run into one while meandering about space. They generally consist of various objectives, which will usually culminate in beaming down somewhere for a little ground combat. I've encountered two of these so far and I wasn't disappointed by the scope of them. I can see guilds doing these in groups of five or ten people, because a well coordinated group can sweep through them much more effectively -- plus it's more fun that way.
I've come away from my early impressions of STO with a very positive feeling. Being a beta, it's impossible to discuss level pacing, enemy difficulty and other aspects of the game that are still in development. However, I can say that my time spent with the game seemed to slip away into the late hours of the night and that's never anything but a good sign. Time will tell how everything pans out for Cryptic's second project post NCsoft, but -- and you'll have to excuse the pun -- the stars seem to be aligning in a promising position.