A great work of art is one that truly moves and inspires you. You yourself must be moved. Don't look at art with others' eyes. Don't listen to music with others' ears. You must react to art with your own feelings, your own heart and mind.
If you allow yourself to be swayed by the opinions of others- "It must be good because everyone else likes it", "It must be bad because no one else likes it"- your feelings, your sensibility, which should be the very core of the artistic experience, will wither and die.
To enjoy art to the fullest, you must abandon all preconceived notions, leaving a blank slate. Then confront the work directly, with your entire being. If you are deeply moved, then that work is, for you, a great work of art.