this is cool! :) great visual design too.
I enjoy casual games like this. in fact, I think I might actually learn how to use the keyboard without looking now :P
I agree with having some sort of incentive to play longer. It doesn't have to be ranking up difficulty, combo meters, or points. Could be something like different firework types / trails / paths after awhile, different backgrounds, etc.
I did notice that after I tried to make all 4 fireworks explode at once in one action, now only 3 letters show up and the 4th firework can never be sploded.
