Ran fine on my Vista machine at home.
Played through to level 4 without dying, had maxed out powerups.... then a big block fell from the ceiling without warning, and I died...... 0_o
Maybe the balance needs abit of tweaking ^_^
It desperately needs sound too.
Oh and more exotic power ups

Apart from that, good game!
Out of interest, why did you write the game using .net?