It does seem a bit like double standards, but we should remember that Halo 3 has the whole multiplayer thing going for it, and the campaigns in both games are roughly as long. The styles are also very different, and Halo's hype is orders of magnitude above Metroid's.
A point of difference is far from outrageous, but their reasons sound very fishy to me. I can't be bothered to read both reviews, so I'll just assume they're slightly out of context. =/







