I like the fact that this game is challenging at first but I think it's too challenging.
Getting from level 0 to fighting Gods with your own rainbow deck can be a really frustrating experience. There is like this huge wall you have to climb over, after which it's smooth sailing. After you start winning upgraded cards, you basically never have to worry about going broke again. But before you get to that, getting money to buy more cards can be difficult because you lose money when you lose a fight.
I remember when I started out, I went broke a couple of times and had to go fight level 1 and 2 all over again. Now I don't mind that so much, but there are a lot of players that might quit because of something like that. This is an amazing game and I hope more people would play it. Making the early experience a bit easier might increase the number of players (and developers earnings).