I think "great" songs come in two major clasifications - there are the songs that are technically brilliant - either musically or lyrically or both; and then there are the songs that reach out and grab an audience in some manner that they want to hear them over and over - even though they may not be "good" in a technical sense.

What becomes frustrating is that some of the great songs written just never become popular; and some extremely popular songs just aren't that great technically.

I have some friends who do fire dancing; and was watching one of them one day. He did his first bit, got great applause, and went into a second routine - which, technically was much much more difficult - and he did it well.   The problem is - he knew it, I knew it, maybe one or two other people in the audience knew it; but visually it's a dud. the much simpler routine he had done first as a "warm-up" was VISUALLY much more impressive - even though technically it was nothing. He lost most of his audience during the second bit - and was very bitter about it afterwards. and yes, given the right audience - the second bit should have gotton more applause. But life isn't always like that.