I don't often visit metacritic, but when I do, it's usually for a game that I am not sure about purchasing. I typically avoid most of the glowing reviews (i.e., 95+), as well as almost all of the user reviews, and generally follow the professional sites that try to be the most objective in their reviews (understandably, there will always be a degree of subjectivity).
I think that an important aspect of reviews is adherence to a site's rating methodology. As harsh as the 1/5 score for Halo 4 is, it ultimately adheres to that website's rating methodology, which is this:
http://www.quartertothree.com/fp/our-ratings-system/
5 Stars = I loved it
4 Stars = I really liked it
3 Stars = I liked it
2 Stars = I didn't like it
1 Star = I hated it
It's clear that the reviewer hated the game, and rated it according to the website's methodology (although I personally do not like their overly simplistic rating system).
With that said, I'm not against Metacritic including outliers in their scores, but I would hope that Metacritic would be selective enough to choose sites that have more well-thought out methodologies than that particular site's simple one.
