A wonderful game.
This is very much a fast paced tower defense game which has quite a good difficulty curve.
The only flaws i had was there was a sound loop of tesla's main attack that carried on throughout the game, even in the menu also was very short.
Albeit short those minutes were great fun.
graphics: Perfect with nice background, destruction on the playground and smooth.
Difficulty: started out just with my mouse but on the second round knew i had to use the numbers as it is very fast paced. nearly died at one stage but worked through the game with zero deaths so could be a tad harder (and by tad I mean add like 10 more strongish enemies so very small boost in difficulty)
Music/sfx: except for the electric loop, everything fit in well.
Story: Who needs one when you can just throw the player straight into the chaos... I usually don't agree with this but in this case I think it worked. Putting in a short "explain what the hell is going on" would have just been a waste of time for you and players (might have increased the play time but would slowed the pace of the game).
Gameplay/controls: simple yet very effective. easy access to placing towers quickly and using power attacks.
Medals: way too easy to get. add something to make it harder so people have a reason to play it again.
All in all fix the loop, add a never-ending mode (with some sort of health regeneration in it) or something to increase the play time and then this game will be perfect.