It's actually very fun once you know the mechanics. My only problem is that the ships's movement is very slippery. It makes progressing the game difficult when the fun really kicks after player unlock ships and acquire a lot of control commands.
One more thing, consider differentiate the ships not only by the shape but also by the color if it's possible. Hard to tell when they overlaps
Nice to know that the game can be played with 2 people :)