Great game, but I feel the energy costs are not really balanced at the moment. High-cost cards are almost never worth it, because just playing two 1-costs is usually stronger (because you just draw on play). And if you get a decent amount of 0-costers, you can just move all your higher cost cards to the left and spam R as fast as you draw cards. Because the amount of cards in the deck is fixed and not much larger than the hand, 3 0-costers + 2 1-costers is already enough. With 3 freezes, 1 0-cost shoot twice and a rotating 1-cost card, I was able to reach an infinite loop that just draws freezes faster than enemies can unfreeze (not gonna say that wasn't really funny though).
Maybe drawing on a timer (instead of on play) could make higher-cost cards more attractive, would probably require some rebalancing though.