I haven't played around with it that much but for now they got out upgrades for the Medic and for Pyro. Of course there supposed to add the rest of the classes in the coming updates. The Pyro class can now get a flare gun instead of a shotgun and they can get a axe with barbwire on it also. I think once you have unlocked an upgrade you do get to keep it.
Everything from the Orange Box. I got it right around the time Beowolf came out. I was sitting through that craptastic shitfest thinking only one thing and one thing only. "I want to get home and play me some Portal." 2 agonizing hours later, I got my wish.