Thanks for the feedback! I think I will add a tutorial slide for the first level as many people have missed the tutorial and the info on the game page. No one really wants to play a tutorial anyways.
The campaign is intended to be difficult but not impossible. Some levels have a little bit of a puzzle aspect to them as well. A few additional notes. The game will usually provide a way to get out of difficult situations. So if the balls are too fast there is a good chance there is a lightning or snail power up incoming. If there are seeker missiles there will likely be a chaff countermeasure power up. Also missiles can be confused be exiting the screen and appearing on the other side as they don't have that ability and instead must arc back towards you. The play through video posted here illustrates some techniques that might be useful.
If you get stuck on a level and want to move past it you might give the Konami code a try from the main menu ;-)