I really love all the different nodes you came up with their different looks and abilities. The game looks and sounds great.
The problem is that I quickly ended up with a million nodes that wrecked every enemy and made me pretty much invincible and started lagging the game due to all the bullets on screen. I think you would be better off limiting the number of nodes a player can get. That would allow each individual type to shine more and it would create more of a challenge (possibly spawn more enemies as well).
Changing up the background a little would also help (maybe use two different tiles and mix it up). It would give the players a better sense of orientation.
But overall great job! This idea has lots of potential and it's clear you put a lot of effort into this game.