1. An idea that has an original element; if it's been done, it's not great.
2. A common thread, musical and/or lyrical, that people react to on a gut level; if they don't relate, it's not great.
3. A killer hook. You need one line that sums it all up and concentrates the message and the emotion into one climactic moment; if there's no payoff, it's not great.
4. A well-reinforced hook. The story should create a tension that peaks or resolves itself in the hook. Also, people have to be able to remember what your song is called when they go to the record store to buy it or call up the radio station to request it; if there's no build and release, it's not great.
5. A great story, even if it's a simple emotional snapshot, needs to have something interesting to draw the listener in; if it's boring, it's not great.
6. Real feelings; if it's fake, it's not great.
7. Well-crafted lyrics that get the story and the feelings across in a clear, accessible manner; if nobody understands it, it's not great.
8. A catchy melody, one that is not only memorable, but also has prosody to complement the lyrics; if it doesn't “sing,” it's not great.
9. A performance and production that captures the essence of the song; even “Stardust” sounds like a bad song when some tone-deaf tequila chugger tries it at karaoke night; if it sounds awful, it can't be great.
10. A great publisher or plugger to get it cut; a song isn't great until it's out there doing its job, touching lives, and earning money.