Common Elements in the best and worst musicals.

Iv'e been asked to do a presentation about musical theater for a group of actors and dancers, that have very basic knowledge about musical theater history.
Now, my lecture is just one of many that they will attend, and I don't want it to be boring, so i'm doing it in a concept of "how to produce the best and how to produce the worst musical"

So I started to think of elements that can be found in some of the biggest hits, and flops(for example: Sequel to a musical as a common elements in flop musicals)

Can you please help me think of some?
Thanks:)

Common elements of flop musicals: Frank Wildhorn

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Oh! I almost forgot about Vampires, thanks:)
anything else?

^ uh, what?
That's just all sorts of not true. Let 'Em Eat Cake? The Best Little Whorehouse Goes Public? Bring Back Birdie?

A great show curtain

Good Musicals have:

Established and developed goals, obstacles and resolutions for their characters and plot(s).

Songs that either comment directly upon the action of the piece, or that propel the plot(s) forward to the next plot point or, ultimately, the resolution of the plot(s).

Lyrics that actually rhyme.

Characters who stay true to themselves (in the sense of how they are written and performed) from scene to scene.

Wit and intelligence.

A Leading character or characters you can care about.