Great game, I say.
Well, I have to say, the plot of this game isn't original. It's not the first time outer things want to destroy the World. But, I have to say, the gameplay is unique.
The idea to draw a barrier againist meteors is an idea that attracts me very. So I'd basically give the gameplay a 9 (I dislike 10s. It means perfect, and sadly, nothing is perfect.). However. There are sometimes the barrier draws itself a little bit after you press and drag the mouse. So it gets an 8.
The graphic part is really good. I love the space, the barrier texture, and the meteors. I would prefer the Earth not to have a .JPEG format, but it's still nice to see. So it gets a 9.
Now, the sound is a bit worse. Personally, I don't really like the song, which repeats himself over and over. Same happens with the meteors' impacts. So it gets a 6.
The fun playing this game? A lot. I got addicted to it in matter of seconds. The gameplay makes it be like that, so methinks one could be playing it a lot of time non stop. So it gets a 9!
All in all, an 8.25, but here it's an 8. I love this original idea and hope to see more from you. You could work the sound and graphics part a bit. Even though it may make the game run slower, it will be worth it!