When it comes to monster books for RPGs, it's pretty much a given that the number of monsters presented is inversely proportion to the amount of information given about each one. Which is to say, you can make a book with lots of monsters that aren't described in great detail (like the D&D Monster Manuals produced for 4e) or a few monsters described in great detail (like the Riddle of Steel supplement Of Beasts and Men). The Hellfrost Bestiary is a bit of a mixed bag in this respect, but in general trends more toward more monsters with less description.
Personally, I don't think this was a good approach. Despite the prevalance of common fantasy tropes in Hellfrost, the PG and Gazetteer nonetheless present a setting with a very strong flavor. It doesn't feel like Generic Fantasy Setting #1 covered in snow. And I think the Bestiary could have gone a long way toward enhancing that particular feel and separating Hellfrost from the glut of fantasy settings on the market. But its success in this respect is limited.
There are some excellent entries in the book, monsters that feel very much like they are *Hellfrost* monsters, not D&D monsters with a white coat and "Ice" stuck at the front of the name. In particular, the Fey entries are very good as are the monsters that seem to be drawn from Norse and Germanic myth (and if they aren't actually drawn from myth, kudos to the writers for making them feel like they were).
Other entries are less impressive. Some are interesting but not particularly evocative or inspiring. Most of the undead fall into this range, which is sad because I feel like undead are important in the setting. Monsters specific to the Hellfrost seem much the same. Others are just stock-standard fantasy monsters. Except for a sidebar on tribal traits (which is very cool), the orcs could have been drawn from nearly any Savage Worlds fantasy game.
Leaving aside the entries I outright disliked (the manticore -- a Persian monster -- and the various demons that don't seem to fit the setting at all), the book seems like a mix of interesting, evocative monsters and, well, filler. There is a plethora of ordinary beasts and monsters with "Ice" or "Frost" or "Hellfrost" stuck in front of the name, and while some are cool, others are frankly silly (the Ice Ooze and the manta-like creature that hides under the snow come to mind here). It honestly gives me the impression that some of the entries were written just to take up page count or meet some arbitrary number of monsters planned for the book. And given that it's so easy to come up with Savage Worlds monsters on your own, the "filler" entries seem even less necessary.
All that said, this is still a useful book and an enjoyable read. As another reviewer noted, the art is good but sparse. The book isn't quite what I was looking for, but even the pickiest of GMs should be able to find a few useful monsters in here, some of which can spark an entire storyline. As for me, I wouldn't say I'm disappointed in the book, per se, but it does lose a star for missing a great opportunity.