The Nightmare Before Christmas follows a very common trope called Home Sweet Home, but it does so in an unusual manner by making Jack initially bored with success, rather than having them be unsuccessful or an outcast.
Stories like these follow a general progression:
The character longs for something else
The character goes out to find that ...
I suggest you read a similar answer I gave because it very much hits on the same overarching points I'm trying to make here.
The first and third picture (Jack, Jack + Sally)
The overarching storyline is about how Jack initially longs for something more than Halloween, but eventually reinvigorates his love for Halloween and returns back in full force.
For a couple of reasons
They were making great money, compared their previous income, but coming from modest means, they were still frugal in their lifestyles. They could have afforded to buy their own booze and drink it, but instead looked for an opportunity to steal from their employers, instead, for instance. The accumulation of increased income had ...
There are some brilliant ideas about what the final shot means.
Without a confirmation from the director, which I've looked for and not found yet, I personally felt the following was a great analysis, by Jeff Saporito: (my emphasis)
...The fact that Glass turns and stares into the camera is also an interesting directorial decision. Some interpretations ...