I DEMAND A SEQUEL!!!
The controls, card system, balance, pacing, and everything were superb. Everyone else has stated how much they love the game, so I won't go on about that, but I'd like to give ideas about a sequel.
All of the bosses, while cool-looking, were totally static. If they had parts that moved or that could be blown off, I think it would only add to the fun. Did the three different barriers have anything different from each other? I didn't notice. Also, maybe you could add SOME permanent upgrades to your ship, instead of just having swappable cards only. Also, the lack of upgrades was disappointing; there were the gun upgrades, and then the barriers in the second or third level, but health ONLY dropped in the first few levels, and there were no speed upgrades, no temporary upgrades, such as widening the beam/adding spread to it or temporarily making it so your beam went straight through enemies, and things like that. Also, I don't think it was a good idea to have all of the money on the screen slide to the left.