Nice game, but bad layout on instructions.
Since the instructions didn't feature the shield and color bomb I didn't get what those were. When I first saw those explanations in-game I just thought "Pftt, pesky level up stuff. Nothing important" and I don't think I'm alone with this. When I actually noticed the color bomb I just thought "Oh, look. powerup. Press space, right?" Nope. But I got into the top 10 (for now) without the color bombs anyway ;D
Long story short: More obvious controls and instructions harder to not notice for the people who just want to play an action packed game to the full without much thinking.