Halo Zero is a fun game, but it is way to short.
The graphics do not look bad for a free to download 2d side scroller game, but they could of looked better.
The sound is pretty much the same sound as in Halo 1. The music is also the same, which is not a bad thing, I have always liked the musci in Halo.
If you want a free, quick to download, easy, and good 2d shooter in the Halo universe, then you should give Halo Zero a try.