Lyrics should sound like real people talking. Every syllable and sentence should have the stresses in the right place (you know, like how people have the stresses in the right place when they talk). The words have to work perfectly with the music. The music is the delivery, the pace, the emphasis, the beauty. If there are rhymes, they should be perfect rhymes. Heavy rhyming gives the lyrics structure, and lets the listener know that the person talking is either smart or calculating. Lyrics can also be fun, poetic, surprising, and clever.