Chris Giarrusso made his name drawing the Mini Marvels cartoons that appeared in various Marvel Comics. His art is fun, energetic, and reminiscent of Bill Watterson's Calvin and Hobbes work. G-Man is his foray into creator-owned characters, ones loosely based on his own family experiences (I am guessing). Here is an interview with Giarrusso about the book where he talks a little about his influences.
G-Man is a young boy who gets superpowers from a magic cape. He gets his name from the fact that no one can pronounce his last name. His big brother is Great Man, and they have a pretty normal sibling relationship. That is, they get on each others' nerves a lot. Their relationship really gets fleshed out in the series of "Mean Brother" (drawn by G-Man) and "Idiot Brother" (drawn by Great Man) comics that appear throughout.
This book chronicles their misadventures and it is full of entertaining characters. These include a powerful wizard, superhero friends from school, and G-Man's parents and teachers. The stories are whimsical and enjoyable, such as the one where the wizard sends the boys on a quest to retrieve his magic chalice. This grand quest ends before it even begins because Sparky the Swift finds it in the kitchen sink. Apparently, the wizard is lax with his dish washing...
This volume, published by Image Comics, has been well received in general. This review from Snow Wildsmith points out the fun points about the book, even if some of them rely on mild potty humor. John Hogan states that this book would be enjoyable for both older and younger readers. It is full of in-jokes for superhero comics fans but also works well as an introduction to the genre.
Giarrusso's official website is chock full of surprises. It has a good collection of his artwork, story samples, sketches, and a few fun games to play. Fans of Asteroids and Breakout especially may be pleased.
An extended preview of this volume is available here.