Needs more work
This movie was, in overall, not so good.
The graphics were made as if you tried to draw things from memory when you aren't good at that. Try using reference pictures for your Halo material. Plus don't try to make everything look like a platform game. Not chief from the side and grunt from the side. Or marines facing the screen.
The animation was pretty slow. I don't think people want to see a Masterchief slowly walk past the screen with nothing happening. Try to make it faster.
As for sound, it was not so good either. There were loops and complete soundtracks used, which is not really appreciated. Try putting some variety in the sounds. Plus it's best to use stream sounds instead of start or event sounds.
And humor. A bit weird, but I did like the walmart sign falling.
In overall, I regrettably have to say it's crap. I do, however, look forward to your future creations if you get better at Flash.
For the time being, I suggest you practice more in Flash before you submit things to a site such as Newgrounds again, because the bar is very high here.