Thanks for playing! I ran out of time for controller support sadly, but it would probably be quite a good thing to add in! Congrats on guessing the pickup names (almost) - [W] was meant to be "wave" ;)
Energy is what is increasing the power of your weapon. I'll need to make that and other things much clearer, most likely through a much better tutorial.
And to fix that last issue, I have plans for a much better enemy spawning system that means you won't be waiting around as often.
Good luck if you do go back for the good ending!