definitely a 'companion' piece This book is simply a sort of addition to the main storyline. It's not that memorable, though definitely worth reading of you liked Infinite Crisis.
Enjoyable (but Unnecessary) "Companion" If you enjoyed "Infinite Crisis," you will delight at the wall-to-wall action in this collection of specials. Fans of Bill Willingham's "Shadowpact" series shouldn't miss the Willingham-penned section here; likewise, fans of Greg Rucka's "Checkmate" series will enjoy his "OMAC Project" story here. If you're not a fan of any of the above series, though, you can probably skip this book.
Interesting...but not worth buying This title collects four specials that take place during the events of Infinite Crisis. It answers lingering questions (like how Kyle Rayner became Ion again) but it really is a dull read. I recommend flipping through it at your local book store to get a feel for what's going on but it's not something I would add to my collection (unless of course you're a hardcore collector).
Day of Vengeance: The Ninth Age of Magic Phantom Stranger and the new Shadowpact rebuild the Rock of Eternity and recollect the Seven Deadly Sin Demons while Nabu (without Doctor Fate) does battle with Spectre. The only half interesting thing about this special is Detective Chimp trying to become the new Doctor Fate.
Rann-Thanagar War: Hands of Fate The war wages on, and it is revealed that Superboy Prime was responsible for Thanagar falling out of orbit not Rann's planetary transport as the Thanagarians once believed. The two groups must form a temporary alliance to deal with a much larger threat. This is the best story in the collection simply because it explains how Kyle regain the power of Ion.
The OMAC Project: The Lazarus Protocol Brother Eye has crashed in the Al-Khali Desert right in the homeland of millions of terrorists. It holds detailed information on every super hero on earth. To prevent this information from falling in the wrong hands Batman sends Sasha to destroy it...but was this the wise choice? Can she resist Brother Eye's control? If you want to know...pick up the book. I'm not going to spoil it for you.
Villains United: A Hero Dies But One Lex Luthor masterminds a global prison break (including Metahuman prisons like Blackgate, Arkham, The Slab, Alcatraz, and Enclave M.) It is up to Oracle and J'onn to mobilize every available hero (most unknowns) to come to the earths defense. The only noteworthy item in this story is Catman straddling the fence between hero and villian.
Overall, This collection is worth a flip through...but in my opinion it's just too dull for my $10.
A nice side piece to Infinite Crisis The Infinte Crisis Companion is just as it's title implies" a companion to the mega-event Infinite Crisis that provides some answered questions to some of the loose ends of Infinite Crisis. Collecting the various one-shots based on the mini-series leading up to the Crisis (Day of Vengeance, OMAC Project, Rann-Thannagar War, and Villains United), the Companion tells side tales taking place during the main storyline of Infinite Crisis. Bill Willingham, Greg Rucka, Dave Gibbons, and Gail Simone all return as we witness the Phantom Stranger, Zatanna, Dr. Fate, and other mystics unite to take down the renegade Spectre in the first story, which also sees a dynamic fight to the death with Dr. Fate and Spectre, and leaves the door open for the fate of Captain Marvel. In the second story, Green Lanterns' Kyle Rayner, Alan Scott, and Kilowog are in space with Hawkman, Hawkgirl, Adam Strange, Jade, Donna Troy, and others in an attempt to thwart Alexander Luthor, and reveals how Kyle Rayner transforms back into Ion. The third story finds the downed OMAC satellite not going down without a fight, and reveals the fate of Sasha Bordeaux, while the final story finds Luthor's society of villains taking on Green Arrow, Martian Manhunter, Black Canary, and a host of other heroes in a gigantic battle to the finish. The art varies from story to story, the best being from Ivan Reis whose pencils are always a welcome sight. All in all, the Infinite Crisis Companion may help novice Infinte Crisis readers with all the mayhem going on in the story, but for those who are a bit jaded with Geoff Johns' series, this won't sway you at all.