Ehh...
The music was terrible man. Just use the music from the preexisting 5 Halo games. Or something just orchestral would be fine, but not whoever the fuck crooned this thing out.
The Chief sprite was good, his jumping was a tad laggy and he fell way too fast for how little he moved forward. I ran into an enemy from jumping over it because of that.
The background looks bad, if you're going to use a sprite, then make the backgrounds match, at leats that's my opinion.
Also, I sometimes jumped through a platform on level 3. Seeing as how it would be impossible otherwise, I can't complain, but it still seems very unnatural and...I dunno, lazy?
But...please... If you don't take any advice, please at least add a damned mute button.