Nice idea.
The music was very up-tempo for a game that starts out this slow. But I recon things wil speed up once you've progressed far enough.
I believe this was a very refreshing idea, using the letters. Still, it lacks detail, it doesn't look very pretty wich may sound unimportant, but remember that you have to look at your screen for a pretty long time. :)
I hope you'll find the time to improve things by adding some more stuff (weapons, upgrades, etc) and make the outlook a bit better.
On a sidenote, I found it hard to read the instructions properly, plus there was no way to tell what is needed exactly to advance to the next level and you also might want to explain what a bomb does exactly. I just avoided them for some time before I realised I can shoot them to collect them. :)
Anyway, i hope you make more. 'Twas good.