We tried watching the movie (which I'd never heard of until about a week ago), and just didn't get it. But we decided to try the show anyway since 40-somethings in wigs playing teens seemed like an amusing idea. And it was! For me, that joke never got old. Besides that, there were some great parody story lines, playing on old TV and movie tropes, that I found very funny.
-Standout Actors-
The show is worth watching for Paul Rudd and Elizabeth Banks alone. They both went hilariously over the top, plus their story lines were among the funniest. Kristen Wiig, Josh Charles, Chris Pine, and Michael Cera were standouts in smaller roles, for the same reason.
-This show is polarizing -- for a reason-
Some people won't get the humour here, perhaps because they just don't appreciate irony and absurdism. But maybe there's another reason
I think some people haven't been exposed to all the cheesy after school specials and movies of the week that this show is parodying. TV has become pretty sophisticated in the past decade or so; it's not quite as innocent (and in some cases, silly) as it used to be. And if you're not familiar with what's being parodied, it's hard to get the joke.