Yotsuba&! is one of the funniest and most charming manga you will ever come across. It contains none of the stereoptypical robots, ninjas or scantily-clad heroines, just the everyday adventures and interactions of a green-haired 5 year old girl as she discovers the world around her. It is a little like Calvin and Hobbes in how it finds humour in the way adults and children perceive each others reactions to things. Yotsuba herself is naive and enthusiastic, and frequently bewildering both to her father and to the three girls next door. People sometimes can't resist playing tricks on her, as in this volume where she encounters a "robot" (okay, I lied about there not being any in this series; but this one is made of cardboard!), and she is always determined to take out revenge once she realises what is going on - usually with hilarious consequences.
There is no plot, rather this is structured as a series of linked stories or incidents. A few stories seem to end a little abruptly, as if the author reached the end of a page limit. Yet, despite this, I am still eager for Volume 6, and wish ADV would fulfill their promise to release it.
On first reading, I thought this series was going to be a bit too cute - I'm not a huge fan of little kids - but my fears were unfounded. A strong cast of characters and mischievous humour make this at least as good as Azuma's other great work, Azumanga Daioh.