Well...
This is good for a first video, but you need a start/replay buttons so the music wont keep going over and over again and tehn it just sounds ugly. Secondly it looks like you drew some of these characters in Microsoft paint, so maybe try to learn how to draw in the animation program you are using.
It's an ok video
The graphics were so-so, they did seem to get better in the end when you introduced the alien. I liked the music; however, each time the flash reloops and starts over the music just sounds worse and worse, like it's trying to start over each time but doesn't succeed. All in all, if it cleans up a bit, it'd be a decent video.