Power Girl finds herself transported back to Earth-2, a world where her old friends, Helena Wayne-- the Huntress and the rest of her old team, Infinity Inc. are alive and well.
At first, she believes she has finally come home-- to the alternate world where the 1940s DC heroes lived, prior to the "Crisis on Infinite Earths" that put them all on one planet (and eventually led to many of the Earth-2 characters being killed off.)
But she eventually discovers something wrong with this Earth, leading to some shocking twists to the story.
One thing that readers should be warned about-- this is a continued story. This is not a self-contained tale. It ends with a cliff-hanger, setting the stage for a wider story that will inevitably involve the other JSA members. Those who thought Power Girl's status would finally be settled in this issue are in for a big disappointment.
As long as you can get over this aspect, the story is interesting enough. Old-timers will get a kick out of seeing some of these old characters again. Fury, Silver Scarab, the Star-Spangled Kid, even the original Dr. Fate and Spectre. It helps a lot that they got Jerry Ordway to do the art. He gives them a look that closely harkens back to the Golden-Age but with the fine detail and styling equal to any modern comic.
There is even an interesting story of Huntress tracking down a decrepit Joker which helps reveal the changes that the character has gone through, ever since Power Girl vanished. The Joker sub-plot is interesting enough on its own even though it eventually proves to be nothing more than a red herring for the big story about Power Girl.
So yes, this book was fun to read but mostly for the nostalgia. It really looks like they are stretching this "Earth-2" thing out, perhaps to the point that people will get tired of it. As it is, we have the whole affair with 'Gog' to deal with-- not to mention the eventual ramifications of the Final Crisis. It is hard to sustain interest for that long.