My overall impression from years of reading them is that if you look at only "helpful" reviews you will filter out negative ones disproportionately to their actual helpfulness, presumably because of a human tendency to dislike negativity. One workaround is to look at, say 3-star reviews (these tend to list both pros and cons) and sort just the three star reviews by helpfulness. There are other workarounds. The first thing I usually do is sort by "newest first" and skim a couple of pages of those. Edit: but checking the Amazon page, there are only 23 reviews in all for that particular book, so, you can just read all of them, which you seem to have done.