Is currently in closed beta, invites going out in waves. Judging by how many I managed to attract to the first game, I figure it'd be worth it to get a post going about the second:
http://dungeondefenders2.com/blog/
Punch in your email address and confirm with the link in the email to be added to the queue.
Plugged my email in, if I'm lucky enough to get some invites I'll send one your way.
Well that would explain why I was able to get the first one and all dlc in a humble bundle for only $10
I did plan on buying this game when it came out ^^