Region is one of the best survival manga out there, it's gripping, its a fair length but not too short and not so long the story deviates, my only complaint is there isn't more of it.
Story - Kanon is a rebellious high school girl who hates her father, Ryuuto (Kanon's younger brother) is a geeky primary school boy who is bullied by his classmates and their father works for a power company. The story is all about Kanon as she sees the emergence of hundreds of rats in the city centre, she immediately goes looking for her brother who is at school and the story of how they try to survive is shown. At the same time, Kanon's father has encountered similar problems and immediately goes off in search of his children, his story focusses on finding them.
Art - I love Yuki Fujisawa's way of drawing people, good people are good looking, bad people are ugly, I can't get enough of it.
Characters - The characters, as with all survival manga, are excellent, you have clearly defined good and bad characters and watching them live and perish is more fun than a child with a cardboard box. There is character development, loads of it, but explaining it would spoil it, suffice it to say, she is no longer a brat by the end, but she keeps some of her childish objections and stubborness which I think is nice.
Overall - Hands down the best survival manga I have read and I've read most of them out there.