Really properly fun game. Even just playing on Medium I found it quite challenging. I could get to the last 2 levels without losing any ships but at that point I had to sacrifice 2-3 to win. I love that it required that amount of strategy though. And I had to adjust the way I was playing as I went along... and met different enemies.
Graphics were awesome. But the game has room for improvement also. I really hope you make another one of these.