Its short enough that you dont mind watching it even during a binge. It occasionally changes so its actually worth paying attention to, and the audio fills fans with such nostalgia that it really amps you up and gets you in the mood to watch the rest of the episode.
I guess all these points are technically true for most adult cartoons like simpsons, family guy, american dad, rick and morty, but my personal choice is Futurama
Gravity Falls. https://youtube.com/watch?v=X2DUpDxFJyg
It introduces all the characters perfectly, sets the scene for the show not spoiling anything and showing that this show that seems it's for kids hides something more adult within.
Edit: The song is damn amazing as well.
Mighty Morphin Power Rangers
Westworld. That intro gives me chills every time.
American horror story gives me an uneasy feeling watching it the first few times during a new season. I kinda like it.
Seriosuly so much fun watching that as a kid.