Simple, familiar, engrossing structures. Not too much waffle with form. They have a beginning, a middle and an end, they have an audience. They work, they're streamlined from generation to generation, they evolve and improve. I've always wanted my songs to have that sort of classicism too.
People now are too easy on the avant garde, they think it's lending pop some sort of dignity.
In fact it may be ruining pop's ability to entertain. David Bowie hasn't made a decent record since he forgot how to tell stories. The trouble with Classical Composers in the Romantic period is that they're too often tarred with the brush of local nationalism. Sibelius and Finland, Elgar and England. It was music for the jet set, or at least the carriage and horses set.