Interesting
Well it was a good game i suppose, and it did have an addictive quality to it, although after i reached about 50 or so it started lagging so i was able to grab the orbs well before my invincibility ran out, so the more i managed to grab, the more enemies spawned which in turn prolonged my invincibility due to the lag.
I suggest including a story perhaps why your character is forced to grab these orbs, or perhaps you make it so he has to maneuver through a maze grabbing these avoiding the enemies keeping with the same concept of with each orb another enemy spawns until he collects a certain number to open up a hole somewhere in the level that you jump into to move onto the next one which in turn pushes the storyline further.
Then you might want to include a certain weapon that can only be used 1 or 3 times per level that kills the enemy or renders you invincible temporarily so you can get passed them. Then maybe include npcs that you interact with, buying potions with the orbs you earned.
Then maybe you want to create a boss that forces you to do something in a certain order or perhaps draw a design as it tries to maul you. or who knows, maybe digging around it until it falls into a pit.
Who knows, there's a million ways you could go with this game, i hope to see it go somewhere great. If not, well, that's yours loss.
Goodluck,
Glum