Niall all characters are unlocked from word go, that is a major component of the game, being able to switch your team composition on the fly to respond to what the other team is doing, which is a change from the TF2 formula with many more "classes" available to each team.
I have already purchased it and was in the beta weekend way back, so granted I don't know the changes or new maps etc, but it was a ton of fun then.
I see it as not my new WFA, that won't happen again, but definitely my new go to for a quick match of something.