They're not fine-grained enough IMO - IMDB's "parent's guide" is great for detailed content information.
Similarly, with game ratings (video- and boardgames, as it happens), I appreciate them, but often they're trying to do two things, rate the game content and the gameplay. They fail often, and I buy outside the ratings, but I'm happier having them than not having any information in that space.
I wouldn't want no ratings for film/TV as that would mean I'd have to seek out spoiler-level information before finding if media was right for what I wanted to consume (or take friends/family to consume). I try my best to see little about the plot of films I'm keen to watch.