It’s tough to judge the measure without understanding the distribution. Uber has to compete for drivers. They aren’t incentivised to throw them away without good reason.

Most people I know default to 5 stars. Anything below means something went wrong.

(I do 4 for nuisances, like odour; 3 for discomfort, like jerky driving; 2 for minor safety issues, like being on the phone; and 1 for major safety issues, like threatening my fellow Pool passenger or nearly hitting a pedestrian lawfully using the crosswalk. Maybe once every few weeks I’ll rate a ride less than 5.)