Yep. Amazon reviews have a tendency to be pretty binary.I'm also not surprised that the response here is more 4s and 2s than 5s and 1s, for a couple reasons. As mentioned, people who go review a product (on any site, and any product, not just D&D books on Amazon) tend to have something they want to say, which is generally highly positive or highly negative - more often negative, in my experience. Otherwise, why bother.
I tend to ignore the 'extreme' reviews. The ones with 2 to 4 stars are a lot better to judge a product.