The Basic Premise
Puella Magi Madoka Magica, or Madoka Magica for short, is a 12 episode anime produced by Shaft and Aniplex. It's the story of Madoka Kaname as she and her friend are thrown into the world of witches, monsters, and magic.
But this series doesn't go where you think it's going. Bear with me for a second.
The first episode opens with our pink-haired heroine witnessing a battle between a giant world-destroying eldritch abomination and a mysterious girl with magical powers. Despite the girl's best efforts, she is obviously losing. A cutesy white long-eared cat creature (later revealed to be named "Kyubey") appears beside Madoka and tells her that the only way she can help is to make a Faustian pact with Kyubey and receive magical powers, taking on the title of magical girl.
Before she can make the deal, however, Madoka wakes up in her bed.
At school, she meets the mysterious girl from her dream (named Homura Akemi) who tells her not to leave the life she is currently living and warns her against getting involved with the supernatural, something that utterly baffles Madoka. This warning is effectively moot as events occur resulting in Madoka and her blue-haired friend, Sayaka, getting caught in a fight between a witch and another magical girl, Mami.
Mami and Kyubey explain that the world Madoka lives in has a secret underbelly full of monsters (the worst of which are the witches, which aren't actually traditional witches, but rather these monstrous abominations that live in "labyrinths"-- pan-dimensional realms of chaos. The only defense against these monsters are the magical girls, young women stupid enough to-- I MEAN BRAVE ENOUGH to take Kyubey's deal. They get one wish and in return they dedicate their lives to destroying witches.
And it all goes downhill from there.
WARNING
Given the nature of the show-- with every episode having some greater revelation or huge plot development-- it is sorta impossible not to delve into spoiler territory while discussing the plot. So I won't. But even discussing the metatextual aspects of the story can be constituted as a spoiler, so if you want to go into this clear, stop reading now and go watch the show.
Madoka Magica is, at it's core, an unintentional deconstruction of the typical magical girl anime. I say unintentional because the creator, Gen Urobuchi, has stated that he didn't mean to make a dark subversion of typical magical girl tropes, he just wanted to tell a good story. Which he did.
The magical girl shows and tropes in question (for those who might not know) are the Sailor Moon and Card Captor Sakura stuff where high school (in this case, middle school) girls attain super powers and destroy evil with the power of friendship and pastel colors. At first glance, Madoka Magica seems like it's just another cutesy girly anime. You would be wrong.
(There's a reason one of the inspirations behind this story was the story of Faust.)
The character Madoka is the typical naive, yet good-hearted that shows up so often in magical girl animes. This, as everyone around her tells her, is not a good thing. She is quickly informed that the traits "innocent," "loyal," and "compassionate" in magical girls tends to lead to an early and gruesome death. Sayaka, Madoka's best friend and deuteragonist in her own right, is the hot headed one who also wants to do good in the world.
Don't let the moe art style of show or any sugary sweet or promotional material you see fool you: this show is the storytelling equivalent to candy-coated arsenic. This series has girls slowly being torn down to the breaking point-- and some characters are well beyond the breaking point when introduced and are running on fumes. Murder, suicide, insanity, gas-lighting and psychological manipulation, and actual, honest to God tragedy are shown and handled expertly.
Technical Aspects
This anime is gorgeous. The "real" world is a mix of pastel colored characters that emphasize the innocence and ignorance of the people in Madoka's life, while the settings and backdrops are gorgeous (especially the cityscapes and Kyoko's church) which can go from warm and evocative to dark and desolate at a moment notice-- but in an appropriate way that serves the story. Lighting and colors are key.
In the labyrinths, the art style shifts dramatically-- and not just from the real world, but between labyrinths themselves as each one is different. They are chaos and the art reflects that. Some have model-free animation and vector art amid weird desert backgrounds, others have cut-out-esque things and swarming watercolor creatures in a mist filled void, or giant dark chasms full of floating pixellated monstrosities, all with the occasional bit of conspicuous CG just to make the whole thing even more unsettling.
At the very least, the art alone is worth watching just for the labyrinth scenes; it is the closest anyone will come to actually being able to animate a bad acid trip.
In Short
This show is superbly written, highly evocative, and leaves you feeling satisfied. It's not dark for the sake of being dark. It tells a complete, logically progressing story that earns everything it does and gives back so much more in return. It's not stupid, and it doesn't assume its viewer is stupid, either.
All the same, don't watch unless you want your heart ripped out of your chest, stabbed through with silver spikes, and then buried under a crossroad at the full moon, because this show will tear out your fucking soul and won't give it back until the very last episode, after it's wrangled every emotion it can out of you.