I see two kinds of Halo Machinima: Those that aim for RvB-ness, and fail, and those that decide they're going to make a three-year long epic story of betrayal and revenge, etc, etc, and end up taking themselves way too seriously and looking like idiots. Neither is nice to watch.
EDIT: Oh, that montage to Enya music was the perfect Halo anything. Everyone needs to just stop trying.