Overall, this game is very simple. (Not necessarily a bad thing)

The gameplay is, for the most part, pretty easy. However, the only enemy that I can't figure out how to defeat is the Pineapple at wave 20.
I wish that the Mushroom Tower upgrades also affected how long it slows an enemy.
Something that visualizes the path that the enemies will take would be nice.

The graphics are boring. High-level towers use almost identical sprites, which is both boring and makes it hard to tell from a glance what level they are. I end up clicking on every tower to check if it's max level or not. More animations/effects would be very nice, such as toppings reacting to getting hit or defeated.

Sound is alright. The sound effects could be more interesting, though. The music is ok, but more instruments would help greatly. It would also be nice if it looped.

For being a game made within just a week, this isn't bad. Keep it up!

(BTW: Why are the medals hidden? Can you at least give us some hints?)

36 Grad, und es wird noch heißer
Mach den Beat nie wieder leiser
36 Grad, kein Ventilator
Das Leben kommt mir gar nicht hart vor
(lyrics from the 2007 german hit song "36 Grad", translating as "36 degrees")

I'm late to the party, but here's a reminder that the soundtrack is both available and really good! They call it an official rip for some reason.
Also, could you add "Freedom Planet" to the tags and/or description in some way? Tagging the character names would be great too. :)

Very unique style on Vibri!