This book forms sort of a trilogy with two other DC trade paperbacks: "Crisis on Infinite Earths" and "History of the DC Universe." All three books are worth reading, but this is the one tailor-made for silver age fans and people who love the Justice League.

Many years ago, DC established that their heroes of the 1930s and 40s lived in a different universe than the heroes of the 50s they were currently publishing -- an "Earth-2."

This book collects the first several JLA/JSA pairings, each two parts and all done with style, class and a touch of that campy silver age charm that still makes the stories a lot of fun 40 years later.

A catastrophe of cosmic proportions has occurred: An alien entity has extinguished the sun itself. How can even the combined power of Earth's mightiest heroes battle the inexorable cold that threatens to wipe out the entire planet?

Robin, Superboy,and Impulse form the team Young Justice. The other team members are Wondergirl, Arrowette, and Secret.  This book leads into the  Young Justice 80-page Giant and the Young Justice ongoing monthly series.

This graphic novel collects DC Comics' limited series of the same name. The premise: All kids 16 and under are mysteriously transported to a seperate reality from the adults. Robin, Impulse, Superboy and the rest of DC's young heroes must find a way to keep order and solve the problem.
This book is great if you're looking for an alternate to all those grim comics of the late 80s and early 90s like THE DARK KNIGHT RETURNS or WATCHMEN.
As an added bonus, there's also a "Young Justice" story in here too, exploring the origin of The Secret, with art by Todd Nauck.  What more couldja want??

There is a lot to like, such as Trickster's P.O.V. Some is old hat. In many places the action was disjointed, perhaps due to the absence of crossed-over stories from other magazines. But overall this is a great read, both for the promised revamping of DC villians and the creation of a genuine long-term player in Neron.