This is a review for the Linux version, running Ubuntu 14.10. Runs perfectly on linux, only minor issue is lack of an exit button.
I was hesitant to pick this game up, due to the artstyle that seemed lazy in the screenshots and the general simplicity of bullet hell games. I was expecting this to be a cheap "So retro" game. However, when it went on sale and I noticed it was published by Devolver Digital (who have yet to back a stray horse) I decided to give it a go. I'm glad I did and I would recommend this game at full price.
This game reminds me of old arcade classic Aerial Dogfight, except with everything turned to the max. You begin with only the most basic machine gun and engine, then when you die you've discovered that you have a new engine that lets you move twice as fast at the cost of turning speed, a few more deaths later you're erupting out of the ocean and obliterating everything with a laser strapped to a chassis which is a nuclear bomb.
The game offers a lot of upgrade potential, it's surprisingly balanced. There's no combination which felt leagues better than the rest, Although your basic machinegun, chassis and engine feel outdated by the end, nothing you have earned will feel pointless.
The constant flow of gameplay challenges associated with each weapon encourages you to diversify your tactics. This prevents the fact that the game only offers one level and one mode from becoming tedious. One downside of these challenges is that the curve on them is a little bit off. The final challenges are magnitudes more difficuklt than the ones that came before it, and something such as defeating a submarine at MAX combo feels far more luck based than it does skill based.
The only real downside I could say against this game is that once you've completed all the challenges, there's not much to do but try for the high-score. That's not even a problem either with a relatively short round time and tight polished gameplay. I can see myself coming back to this many times in the future.