Not bad! This definitely has some potential. The animation is decent and flows nicely and the style of the characters is (somewhat) new and interesting. The voices did okay. They weren't awesome, but they sufficed.
Some soundtrack to go along the video itself would be appreciated (by the way, the music at the START-screen was quite good! What's the name of the song?).
I have only one thing to criticize, and that's the placement of the box. It's corner really shouldn't touch the sky, as physics do not work that way. A placement slightly lower, and it's all good :)
About the microphone issue, there are many ways you can improve the quality of the voices. Most laptops and maybe even desktop computers or tablets have a microphone/recording program you might try. I used it once before, and the quality was high enough to attach it to a video presentation without any embarrassment. Or maybe there are some recording equipment around the school you might use. Ask around!
Meanwhile, I'll be waiting for ALIEN 2.