I'm kinda curious to know what the last two classes are going to be. So far we've got these classes, and here's how I interpret them.
Warrior - Doesn't look like anything different. Tank, DPS role with swords and shields.
Stalker - Classic Rogue
Spellslinger - Kind of looks like your Ranged DPS combo of Mage/Hunter kinda deal. Maybe debuffer as well.
Esper - With the limited information, I think it's a priest like class that can spec Shadow like in WOW. Or maybe it's a Mage like class that can spec into healing?
Two more blank spots. I can see some kind of Engineer kind of class that is a hybrid, healer/buffer/tank or healer/buffer/dps. Then there probably is a class that wield huge ass guns that can tank and dps.
There has to be a pet class, and most likely that will fit in with the Engineer class or whatever it is. Just my guess though, we'll see in beta.