by 'great', I assume we are talking about A to A+ rather than just a B...

to me, whether it is humorous or serious, that means a combination of tune and lyrics...plus subject mattter that captures your attention.

lyrics get an "A" if they are well-crafted--no awkward phrases or careless rhymes just to get 'done'.

"Lorena" is well-crafted, has subject matter that is timeless, and has a tune that is haunting and still singable. So does "Jock O' Hazeldean" and "The Vatican Rag"...of course, not all 'great' songs are to everyone's taste, so that last one will never make an all-time list.

Some songs just miss by a hair-- "The Night Visiting Song" is very good, but the melody is a 'bit' boring, and there are a couple of lame lines.

now, for the entire 43 chapter essay, I'll have to go off and write for a few years.