I say this in a mildly confessional tone, because the show is, as I feel compelled to say aloud every time I watch it, completely ridiculous.
I mean, it's fundamentally musical theater, which is ridiculous at the subatomic level, and the plot holes are big enough to accommodate small planetoids, and the premises that the storylines are built on are just ludicrous, and the drama levels are flat-out insane, and yet somehow the whole mess is just massively, massively entertaining.
I'm only halfway through the first season (just watched "Sectionals"), but I'm really enjoying it. It's funny, though. I feel like a lot of what the show does is pressing obvious emotional buttons, but when does that, it's like it's saying "Hey! Here's a button! I am going to press the button. Are you ready? Here goes!" And then it presses the button -- usually pretty effectively -- and I feel my buttons being pressed, I do, but I also am compelled to make jazz hands and shout out "DRAMA!" and cackle with laughter. Because it is all Just. So. VERY!!!
I hypothesize that maybe the reason that it works is because it's totally straight-faced and unselfconscious about it all. It's like the band The Darkness, which is so completely over the top with its rockin' hair-metal badass self that you think "they can't possibly be serious. Surely they're taking the piss," but there's never any wink or nudge about it. It's either so sincere that it starts to verge on irony, or so ironic that it's wrapping back around to sincerity. And either way, there's the very heavy layer of "yeah, sure, it's goofy and dumb and whatever. So what?" that is deeply charming. Because who cares as long as it's enjoyable? And it is.
So if you haven't gotten your gleek on yet, you should. And for everybody else who's already on board? I get it. The name of the show is utterly apropos.