I think some ideas that would make this game more fun are:
- Remove freeze, all cards should require energy
- Interesting power ups offered every level
- Choose not to switch cards
The current state of the game makes the scaling unsatisfying. You quickly go from 0 to infinite (or die before you get there) because most of the cards are not very good. After you get freezes, you can do whatever you want, but freezing also slows down the game and makes it boring.
It's highly unsatisfying being forced to make your deck worse.
Altogether, a combination of changes that make the player weaker (removing freeze, all cards require energy) and changes that make the player stronger (more and more frequent power-ups, choose not to switch cards) should make the gameplay more fun.
I also think longer levels was a bad idea. Levels should become more difficult, not more grindy. After freeze is removed, level 1 vs level 10 should take the same amount of time, but you obviously must fight more spawns and more difficult spawns.
(got bored at level 68)