Brilliant! But...
Wonderful game!
However, there are a few things you need to improve:
1) Variety of enemies. Maybe you could add Princess Peach attacking? Princess Daisy? The Toads? Also, give the enemies something to make them special. Fast enemies, flying enemies, BOSSES!
2) Turret specials. Think of implementing a choice of specials for turrets: Poison, Splash, criticals etc.
3) Game balance. In the campaign, I buzzed through about 5 waves, upgrading my turrets, no lives lost, and then I only killed half a huge wave. Also, the Free Play is WAY too easy. I build my turret system and nothing will get through for a couple of hundred waves.
Think about this, then make another!