As some have said before, this can actually be a great thing because it is a resource that tells parents what is in a game, leaving the parents responsible for doing the research. Such material online can be easily understood, so no more "Well I didn't know there were hookers in Grand Theft Auto!!!"
However, what undermines any video game content evaluation is whether or not the raters actually play the game and are not just tossing in their own personal biases. Those two factors are pretty much a given because it would be equally deceptive to say that Movie Y has "mature sexual themes" when a couple is just kissing in the background of a shot or the person "reviewing" has merely heard that there are kissing scenes in said movie. As with the adage "Don't judge a book by its cover," don't present video game content (or movie, novel, music CD, ect. for that matter) based on unfounded claims.
But if you're dropping $60 for your child, shouldn't you at least be aware of what that sixty bucks is going towards? If the special addition had shotgun shells and condoms, would more of the irresponsible parents then heed the warnings on the box?!?