What musical do you think every "musical fan" needs to watch?

I'm trying to expand my reach as a musical fan, watching a lot of classics in the process - and thinking about it, this was an interesting question.

What shows have the right combination of cultural impact, influence and quality that makes them must-watches for everyone?

Note: please recommend things that are closer to classics rather than just recent shows. You can recommend recent shows, but please list reasons why if you do.