Many reviewers are biased and judgemental. I prefer to look at the distribution of ratings that amazon shows. Good items have a distribution with one peak, even if it isn't at 5 stars. When ratings create a saddle the product is probably a fluke.
The cute XKCD comic aside, the distribution is also useful because, for certain types of things, a lot of fairly to very negative comments are illuminating even if the average rating is still pretty high. It's not just about polarizing material. If you look, for example, at genre fiction you'll get a lot of fans who give 5s no matter what sort of crap the current book is. But if there are also a notable number of 1s and 2s, that's often a good red flag.
