I liked this one! Though the key pick up sound almost raptured my eardrums, the music wasn't preparing me for such a loud noise.
The theme is handled pretty well. I think it's a good direction with colour coded weapons/bombs required for progression. I thought I needed a red bomb to kill the red enemies, this wasn't true, and then I thought, it would've been cooler if it DID require you to have a colour coded weapon for certain enemies. Also the slime mechanic is cool: enemies just clogging the screen and slowing your movement, I like that!