Well after watching my nine year old make it to wave 50 with absolute ease, I realized it was time to amp the game up a bit. I did some tweaking, and this is what all I've come up with.

UPDATE

Increased the size of the map. Makes things more balanced in the later rounds.

Improved stats, and odds of getting random loot.

Gave the portal god a voice.

Fixed some bugs with enemy AI

Fixed the help screen, so it no longer shows the wrong key while using mouse and keyboard.