There are currently four classes in the game -- Assault (your usual tank and soldier -- Harris told us it was probably the easiest class to play), Medic, Recon (a scout/spy kind of character, that allows for both stealthy gameplay as well as long sniper shots and backstabs with melee weapons), and a class called Robotics, which struck us as a Team Fortress 2 Engineer type of character (in fact, during our gameplay, both Harris and we called it an Engineer, and he shared with us that the team originally called it that during development). Robotics characters have a robotic armor attached on the back of their armor, and can use all sorts of fun gadgets and doohickeys, from turrets to healing points to even pets. We couldn't pass down a class like that, so to duck into our first PvE mission, we chose the Robotics class.
Next up was gear -- each character is granted a certain number of "device points" (we had 15, a midlevel character), and those points can be alloted towards equipping certain pieces of armor and equipment from your inventory. First up, we gave our Engie -- sorry, Robotics character a mace to swing, and that took up four points. We also grabbed what Harris called a "flubber gun" -- it shot a blue plasma-type orb that bounced off of walls and dished out knockdown damage to whatever it hit -- and that put our device points up to around 6. A few turrents, a force field creator, and a few other items later, and we'd filled 15/15 device points, and were fully equipped for battle.
Each class also has three skill trees, and as you'd imagine, the skill trees boost your abilities with the various weapons and equipment that you've chosen. Harris made it very clear that they wanted to make sure players could play a certain spec even if they weren't specced for it, mostly by equipping more powerful weapons of that type -- i.e. if you were specced for support as a healer rather than straight healing, you could equip more straight healing gear, and even though your talents didn't fall in line, you could still serve the role respectably.