Humans are on the decline, and their place is slowly taken by 'fairies': small humanoids who are always grinning and seek to have 'fun'. When they have fun, they invent stuff -- and multiply. Their lack of common sense and their magical technology means they get up to all sorts of wacky antics, with our protagonist, who works as a 'mediator' between humans and the fairies, usually on the receiving end...
She is pretty interesting: looking for an easy life, trying to cover up the times she messes up, not above using intimidation or misinformation to get her way. She is deliciously two-faced, and her grandfather, who acts as her supervisor, knows it (and even gives her advice on it!)
This makes the series the most cynical, bizarre and funny comment on the human mentality I've ever seen. It's like Dilbert with magic. I don't think kids will 'get' the series, but adults will find it hilarious. The bizarre twists introduced by the fairies are wonderful and weird, which only adds to the cynical thoughts of the main character.
Not every episode is great, but they're all at least snickering-worthy. The visuals are lush and paint a detailed picture of what life at the end of humanity's run would be like. The fairies are all distinct as well, which is quite a feat.
All in all, we've had a great time watching this. It appealed to our inner misantrope, making it both amusing and a little bit of a guilty pleasure (because no-one would admit they're a misantrope, right?). I'll give it an 8.