Spent some time with it!
Okay so I played it until level 11, when it got repetitive, which I understand in this genre.
The graphics were simple and didn't confuse me too much.
The powerups are cool, but you can't just survive past wave 10 without them, especially the autofire one.
When there came many missiles on the screen, I became confused of which missiles were actually still coming and which were destroyed, so the blinking line-solution was not the best.
Overall, this is a good minigame.