Now lots of artists put out good song, but what signs tell you that the song you are listening to is great?

For me it came last month when wifey bought the Leona Lewis album. I dont know the name of the album, but I do know she was listening to the first three songs of the album until she knew them word for word, and I am serious. We went to the mall on a Sunday morning at 9am and she didnt turn off that album till about 2am. It was driving me insane. Now I'm doing the same thing with this old school dancehall song by Beres Hammond called "Show It Off". Ive been listening for over two hours now on my ipod and Im still not bored of it, I even put some of the song lyrics in my sig!