Such potential!
This is an almostgreat WASD+mouse game, and is especially satisfying when you line up a shot and hit multiple enemies. However, you should take into account some of the more critical points people have made concerning energy consumption.
To remedy this, perhaps there should be an energy bonus modifier when you retain accuracy and/or hit more than one enemy with a single shot. This gain should be a marginally substantial bonus. This is a hallmark of addictive quick games: high reward and high risk of losing said reward. With a marginal amount of learning, one can enjoy this system.
For easy mode, the energy recharge rate should be very forgiving, so we can nearly breeze through the game. That way, everyone can get a good idea of how the game plays.
For hard mode, your current medium mode will do.
Also, the powerups I did receive are somewhat lame. They do work from a gameplay standpoint, but it doesn't do it justice to awesomeness of the music and the art
Finally, double clicking on the mech is an okay choice to commence boost, but I would simply prefer a button in the HUD area. Maybe its just me.
y.
On the plus, the hitboxes are great, controls are smooth, and your visual design is pretty good.
I take it you put a lot of love into this game, but didn't get enough uninvolved people to test it for you. I guess that's what the newgrounds audience is for.. :)
In parting, your current score of 3.26 is very generous considering the difficulty of your game. I think people would be very excited to have this in a more playable form. I really do applaud your effort! I'm releasing my first game for iOS myself, so this game experience has been very valuable to me! Scale of difficulty is the most troublesome part of game design, don't feel too bad!