I think Rob has it give-or-take a few personal differences.
A good musical score will make me listen to it, and good lyrics will keep me listening to it after a few plays. Nothing makes me like a song more than a good bit of humour; crude, rude, wierd, corny, daft, funky. You name it, humour is the way with all songs! It's what makes me smile still when I listen to Jim Steinman songs - even in the most serious of songs, you still get the "all the signs along the road say "caution, kids at play"". Subtle humour :P
I have a habit of going off topic quick, sorry!
. Other friends I have don't give a monkey about lyrics though....