I don't want to pick a fight, but I think that many of the responses in this thread point to an attitude toward video game criticism much more dangerous than a few low-ball reviews.
You have to let go of this notion that there is some objective truth that should govern all video game reviews, and the idea that "AAA" titles can never fall below a certain threshold. Most of all, you need to abandon the false belief that a critic can't judge a genre or franchise he or she doesn't like to begin with. This in no way invalidates a review.
The purpose of a critic is to articulate a well-informed opinion in an interesting and artful way. That's it.
I think our expectations as fans are a lot more unreasonable than a 20 for Halo 4.