A really quick summary: Cylons are sentient robots; they rebelled against their human masters; the surviving humans are fleeing through space; and both sides like to shoot at each other a lot. This game sets aside the series' complex interpersonal dramas, philosophical and moral debates, and ruminations on the human soul to focus entirely on things going kablooey.
So, as a Cylon warrior, I had fairly limited choices in character customization--some blast damage and armor color changes were about it. However, unlike World of Warcraft or similar games, you spend very little time in Battlestar Galactica Online walking around or dancing. Further, Cylon players seem limited to the metallic Centurion "Toaster" option, not the humanoid "Skinjobs," so there's not going to be any Number Six/Boomer naughty emoting going on. Once the initial choice was done and I had given myself the stunningly original name of "Talos12", I hopped into my Raider and started doing tutorial missions. (In the show, Raiders fly themselves; in the game, Centurions pilot them.)
The first such mission set up the premise for BSG Online. A large chunk of the Cylon and Colonial fleets is sucked into an unstable sector of space, where they must establish bases, mine for ore and fuel, and blow each other up. It's a decent enough way to wedge the necessities of an MMORPG into the show's storyline, I suppose. Other tutorial missions show you the basics of targeting, combat, and mining. Well, sort of. The tutorials could use another pass at polish; I usually figured out what I was supposed to do, but much of that was by hovering over buttons until I got a popup. Other parts of the game, such as the purchase and upgrade system, I just stumbled into.
Purchase? Oh, yes. Apparently, you need to buy advanced weapons, armor, and other systems, as well as better ships, which offer different combat options (speed, firepower, survivability). You buy your upgrades and new ships with currency you earn during missions, such as tylium ore. This is sort of akin to having Air Force pilots pay out of pocket for their planes' fuel and missiles. It's a necessary game mechanic, and getting new gear is always a drive in persistent world games.
Battlestar Galactica Online also includes a skill system which owes more than a little bit to , in that you improve skills solely by expending time--click a skill book, and wait some number of minutes, and, ding! You're better at shooting guns, even if all you did was wander around the hangar bay. It is not necessary to pay real cash simply to advance your character, though that is an available shortcut.