Really a pretty good job and some games that actually make money aren't more complex than this.
Suggestions are just bring in more complexity like power ups or shooting or really this one: have different consequences for letting the energy crystals past you. Like a percent ratio and it does different things if you let too many past you but you can recover from it too is an idea, or things that you can both pick up but -also- it's better sometimes if you don't. Can take this many different ways.
I gave it good marks and gave you an itch follow, if you like the thing(s) on my page(s), consider doing the same.
Cheers!
--D
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