My greatest disappointment with this game is the difficulty, and lack of difficulty settings. The only way I've found to lessen the absurd amounts of incoming enemy fire is to position the ship at the very top of the map and spam the space button; due to the fact that your ship's weapons have limited range, whereas the enemies have unlimited range. Hanging out in the rear in hopes of anticipating and possibly dodging any attack at all is completely an act of faith as there are so many projectiles heading your way, it becomes near impossible for a beginner or amateur to calculate and interpret the correct path to dodge these attacks, and yes - you have to be precise at dodging because one shot and you are dead.
When you die, you lose all power ups, you do have lives but they become irrelevant in the further you progress - namely because you re spawn with the lowest upgrade. That means even if you choose the ship that supposedly is more suited to weapons - if you die, you actually get downgraded.
My recommendation is to add difficulty levels, since not everyone is a god at retro shooters and/or had the privilege of having Neo from the Matrix as their kung fu master. Another suggestion would be to make the downgrading of weapons/speed less harsh. Perhaps one or two downgrades per death depending on what difficulty setting you are currently playing would be a lot less frustrating.
I will admit that I have amateur quality skills when it comes to these types of games, but even still I was able to make it to the 4th or 5th line of ships before I died, every single time.
Good concept and style, even if it has been reproduced many many times in the past, work on the difficulty settings and add some customization to the game play aspects and I think you will be pleasantly surprised with the result.