1) Agreed that one knows a great song when one hears it, as at least a couple others have suggested. This overrules anything else (except #17).
2) A great song makes one bob one’s head, shimmy one’s shoulders or purse one’s lips. Multiples are best.
3) Melody is good. The voice should be considered an extra instrument. The better the voice and the better the melody, the better the chance the song is great. A melody that adds to the song is better than one that simply mimics a riff. To use Black Sabbath as an example, War Pigs is a great song, Iron Man is not. The vocal melody has a lot to do with this.
4) Speaking of riffs, they are good.
5) Good harmony is good. Weird, innovative harmony that is still good is best.
6) At this point I’m reminded of something I once heard about The Smithereens. Their goal was to be The Beatles and AC/DC at the same time. They never came close, but it was a noble goal.
7) Hooks are good. A great musical hook is felt somewhere between the belly and balls.
8) Fast is good. There are great slow songs, but they are few.
9) Heavy is good. Most great slow songs make up in heaviness what they sacrifice in tempo.
10) Mellow is bad.
11) Great music demands attention. One cannot multitask in the presence of great music.
12) Good lyrics help, but good lyrics are not essential. If everything else is there, who cares what the band is singing about? By the same token if everything else is there, who cares whether one can decipher what the band is singing about? Misogyny and profanity are good when used properly.
13) Lyrics ideally take the listener to a fantasy world the average Joe will never experience. Songs about screwing exotic women while high on smack are better than songs about admiring one’s wife as she drives the kids to the soccer game (see pop country).
14) Electric guitars are good. Keyboards and synthesizers not so much. There are exceptions.
15) Musical proficiency sometimes helps, but is never a deal breaker. There are many great three-chord songs. Musical talent alone never makes a great song (not even a decent song).
16) Drums. Let me tell you a little story. I was at a birthday party for a relative last fall. As I sat with my brother at the beginning of the party, the DJ was playing Frank Sinatra, etc. I hate that stuff. My brother detected my displeasure and eventually exploded with something like, “This is the American Songbook! How can you call yourself a musician if you don’t at least appreciate the American Songbook?” While the American Songbook was playing, folks were milling around, generally socializing, not really paying attention. Eventually, the DJ bagged the American Songbook. He began with Hang On Sloopy. As dippy as Hang On Sloopy is, the floor immediately filled with people dancing. Drums.
17) The dark side of dancing is modern choreographed dancing. Modern choreographed dancing has been the worst thing to happen to pop music in the past 20 years. Any sniff of greatness a modern song may possess is negated by choreographed dancing. The two cannot coexist. There are surely great songs that include great choreographed dancing, but none since 1980.