Below 4 stars is bad. Reasons:
Google provides a filter in the play store to show only apps with 4 stars or better. AndroidPolice says that this should "
in theory, should weed out most bad or exploitive apps." BGR, a reasonably well reputed mobile app news source published "
Here’s how to find only the best apps on the Google Play Store", referencing the 4+ star filter.
Apparently
Google takes rating into consideration when searching. It isn't clear whether this would hurt us much, but it can't help.
According to this survey, 3% of buyers will not download an app if it has less than 5 stars and another 35% of buyers will not download an app if it has less than 4 stars, so almost 38% of users won't consider less than 4. Another 39% will not download an app if it has less than 3 stars. Thus 77% of the market considers below 3 star as junk.
Finally
this page says that "According to Google, apps that earn a 4- or 5-star rating average almost 29 times more revenue than do lower rated apps."