This was okay I guess, gets old really fast.
Level 3 seems to be just a blank green screen.
That aside, you've got the makings of a pretty good shooter here. Few suggestions:
The main weapon is so weak that, because upgrades time out, you're sometimes unable to kill anything. How about having main weapon options, like the ones you have, that don't time out, and then extra weapons like the missiles that do? Then you have some choice.
Perhaps instead of timing out, the missiles could have a limited amount of ammunition? Then accuracy would become more important, and holding down fire would drain it faster than employing more skill.
The snake like body is frustrating because it can take hits, and you can't move it out of the way of oncoming fire. Either have it snap around so it's possible to maneuver it, or make it so that only the head takes hits.