I got to try out imperial agent (operative spec) and sith warrior (marauder) yesterday at gamefest on both the Alderaan PVP map and huttball, both were pretty damn fun, definitely enjoyed huttball more though!
Seemed as though the operative had a lot of straightforward single target healing abilities and not much else, though there were quite a few disable abilties and poisons I could use on other players which was pretty awesome. Though when I was playing I zoomed the camera in and it sorta wouldn't zoom out again making it perma first person, so Chris the EU community manager let me have another go, which was nice because the waiting time was over an hour and a half to play.
I definitely had a lot of fun as the marauder, the leap ability is absolutely amazing because you can leap upwards to players on platforms above and and down below which makes you feel like a bad ass when you surprise someone.