Thanks for your feedback! :D
I am definitely changing the floor color next update. Its color messes generally with everything else as my gems are blue and enemies are transparent red. I am taking notes from other games I am inspired to create a better color palette to work with!
I noticed the startup time for learning the game is bit rough. I am now planning on writing a tutorial to resolve this! I also recently redesigned the spawner enemy to be easier to see / read, and to do a visual +audio cue for when the spawn occurs. I hope that fixes the spawn the head problem!
As for the fast enemies that might be the tank chaser types and that is hindsight 20/20 from me. I initially designed them to only be dodged 100% of the time by bunny hopping, but I did not even explain that was possible. I will add this to the tutorial and also adjust the stats of them to ensure they do not get the player instantly.
I got the upgrade screen feedback, and I think I got the fix for this actually. Next update will have the player initiate the upgrade sequence via the tab button. I played with a slow mode, but I think would be easier and not interrupt the flow as much or feel too weird. I will also make sure though a level up is obvious by making the level up sound is audible