I'll never understand why people whine about having to pay for a game. It's $12 on steam. That's 1/2 to 1/5 of the price of other games, and you still get a decent amount of levels for free. How can developers support themselves otherwise? Making games isn't cheap or easy!
I don't mind that there's premium content, though the main game was somewhat short. This is probably a huge dream for the creators, and not many people can make it in this business! I see it as supporting creators and encouraging them to create more and better content. :)
This really is one of the best card games out there, and crazy addicting! I think the only thing missing is a great story-driven campaign mode, which would make the game a little more dynamic and interesting.
Other than that, fantastic job! <3