What are some examples of ‘good’ gamification in the Mary Poppins sense?
imo, good gamification can be found for those applications that actually achieve their goal.
i tried teaching a kid the importance of critical thinking but it was a bore to him.
but then i got him machinarium. he learned a lot about logic and reasoning by playing machinarium on his ipad. he started loving maths later on.

What are some examples of ‘bad’ gamification?
certain gamification focuses too much on enjoyment without attaining the goal. it’s considered bad. once, we were told to play world of warcraft to understand the design of the world physical elements ie rain, water etc. as u may have guessed it, we got so hooked up on the game and never really did the assignment.

Can specific elements that make an example good or bad be articulated?
you know, you could use the REAL training elements here. please find the reference yourself as i’ve totally forgotten where i got it.

Retention – how much of the skill can you remember?
Enjoyment – how enjoyable and engaging is it?
Application – can you apply what you’ve acquired?
Learning – how much did you learn?

a good gamification offers a balance between all the four elements. you end up enjoying what you learn. you can recall and apply it as needed.

a bad gamification emphasizes too much on one element that it disrupts the rest.
too much memorization, you get bored.
too much fun, you are not serious about learning.
too much application, you find it hard to do.
too much learning, you find it too complex and intellectually draining.

hope it helps