I do agree with what you and others says, I use IMDB for trying to "measure" a movie, but as with most things this is about personal preferences, taste, if you like. Not every people will find a certain movie good or bad, no matter what critics says. The same goes for almost everything, I can safely assume that everyone likes cheese but that is not true, but if we put a rating to that it may come up with a 9 out of 10 or maybe more. But that does not mean everybody should buy it and eat it, it just means a lot of people like it, you have to try it for yourself to see if YOU like it.
I thinks the same happens with movie ratings, they're a guide, but no matter what people say about it, you still have to watch it to see if you like it or not. The rating can be a good indicator, but until you actually watch the movie, you just wouldn't know.