When you say greatest cover songs you must be able to define in what ways they are great and what the crucial elements are which define its greatness. The reinterpretation of the song like Rolling in the Deep must be complete and successful and the audience must be taken in by the way it is sung. It must stretch the scope of music in new directions and must be able to captivate the hearts of the audience. If you say a song as a cover song, this must enter the minds of the people. When the title of the song is mentioned, the people must believe that the song belongs to the cover band and not the original artist. Only if the cover band made the song popular this idea would come into the minds of the people. For this purpose the song must be sung in a best way superior than the original one. When people hear such cover songs like Rolling in the Deep cover they will be reminded of the days that they have heard those songs by the original band and they will start loving the cover band for bringing fresh memories into their mind.