Note: Since Google Play has changed the way it fetches the review data, the script currently no longer works. I will look into updating it soon…
Google Play provides only a very limited set of options for sorting reviews of an app and no option to filter by rating. If reviews are sorted by rating, the highest ratings are shown first, and there is no option to sort with lowest ratings first. This makes it unfeasible to find all the one and two star reviews for apps with more than a few hundred reviews, which is actually quite important when considering purchasing or installing an app, in order to identify problems and issues others have had which might be relevant to you.
This user script adds checkboxes to the UI so you can choose to filter which reviews you want to see based on their star rating out of five. It’s been tested with Greasemonkey in Firefox, Tampermonkey in Chrome, and User Script Injector in Firefox for Android.
Note that it currently only works for app reviews, and not books, music, videos, etc. Also note that (currently) only the first 4,480 reviews for the selected sort order and other filters are available to the script before filtering by star rating is applied, so it may run out of reviews to show sooner than expected (e.g. if sorting by rating for an app with hundreds of thousands of reviews, choosing to filter out all the five star reviews will probably result in no reviews being displayed; in this case, change the sort order to ‘newest’ or ‘helpfulness’ to show reviews).
The script was inspired by this question by user @rubo77 on webapps.stackexchange.com which I have answered with details of the approach taken to develop it.