Ola Cabs in India does this. There is still a star rating, but if you give a rating of 5 stars it asks you what you loved most (out of a selection of choices),

Ola Cabs in India does this. There is still a star rating, but if you give a rating of 5 stars it asks you what you loved most (out of a selection of choices), and if you give less than 5 stars it asks you what you were not happy about (slightly different selection of choices). You can pick multiple reasons in both cases. There is even a box for writing free text.