Villains are playable. Even Praetorians are playable. It has all of the content that was available before the shutdown, and even two new Issues that were being worked on at the time. (Not sure if it's just the new Archetype, Power Sets, and such, or if there's actually new missions from I25)
But it's still a test right now- login servers are overloaded so it's tough to get in right now (still managed to handle 700+ online earlier somehow though), disconnects will happen, and characters may get wiped.