The ease of use, it's fast execution speed (compared with other testing frameworks).
It can be used in any programming language for writing unit-tests without having knowledge about Java or C++ languages required by others such as TestNG & Junit4 etc.. I have not found anything yet which i dislike from this tool but if you are looking out something then please go ahead because there will definitely nothing that we don't like here! We were using our own custom test automation solution before so when compared junit was much faster than what ever code written previously!!