Excellent, great fun
I actually gasped when the barrier disappeared. Of course it was going to happen, I just can't believe I didn't expect it. This game is incredibly addicting, and since it's so fast I can't look away from the screen for a second.
But it really needs two things: first, a pause button. Preferably something easy to hit in an emergency, such as the spacebar. This is especially necessary because of the second lacking: there's no way for the player to know how close he is to death. I have no idea what determines a Game Over, and it would really be nice to know.
After playing for a couple minutes on the first game, I began to wonder how much longer the game would last. I'd been letting ships get past, and I didn't know whether the game would keep going for five more minutes, or if I'd die in the next couple seconds. I hoped that the game would keep going (the challenge curve is perfect), but being unable to look away from the screen for even a second, for that long, is a little much.
Of course, all that is only a problem because I was having so much fun playing. Thanks for making something so entertaining!