This is not the place to jump into the Hellboy universe. If you haven't already read [b:Conqueror Worm|102462|Hellboy, Vol. 5 Conqueror Worm|Mike Mignola|http://d202m5krfqbpi5.cloudfront.net/books/1347444064s/102462.jpg|785618], you'll probably end up feeling a bit lost. Hollow Earth, the first and longest story in this volume, builds on the developments of Conqueror Worm, with Hellboy now absent and the BPRD itself in a sorry state. It also continues the development of Roger, a character who'd seem odd at best if you didn't have the proper background.
Mignola had, as far as I can tell, limited involvement with the stories in this collection. And actually, that worked out fine. The writers and artists who worked on the various stories know what they're doing, and their stories fit neatly into the same world as the stories Mignola has worked on. This is helped, I think, by the great cast of characters left behind at the BPRD. Liz has a lot of promise as a character, though nobody seems to know what to do with her. At least there's one fantastic scene with her, shortly after her initial arrival at BPRD, when she's still a scared kid with terrifying and uncontrollable powers. Abe and Roger do great with the spotlight shining more firmly on them than it had been with Hellboy around, and the new character, Johann Kraus, should be able to center some really interesting stories.
Hollow Earth, which takes up most of the length of the volume, is a great story. And the short stories are quite good, too. The quality varies a little there, and most of them end up feeling short. But they do fill in some gaps in the story: Roger coming back to life, Lobster Johnson in the 30s, and Kraus's origin. Better yet is the last story in the collection. The art itself didn't appeal to me, but the story, about lost and vengeful spirits, made for a fantastic read. Vaguely folkloric is a great style and template for stories set in the Hellboy universe.
Basically, this is Hellboy without Hellboy, and very little Mignola. And it isn't a bad thing in the slightest, which honestly surprised me.