Here are some qualities of a good case study:
It is written in a formal, academic language with good grammar and coherent structure.
All of the claims made in the case study have a reasonable basis and can be proven.
The case study does not overload the readers with unnecessary information. It is clear and to the point.
The information is passed to the reader in an organized manner. It has flow, and it is easy to keep up with the extensive academic research.