I found the premise quite interesting.  In the frozen tundra of the Earth, a rift between worlds had opened and creatures are seeping through intent on having their way with the entirety of the Earth.

A multinational force of ultra-trained soldiers acts in this arctic wasteland as a first line of defense.  It seems that during the first World War there was a similar occurrence (that being an invasion of these other-worldly creatures) so the military has been aware of the potential ever since and wants to save the Earth should it happen again, so they sent out 6 soldiers.

On a routine patrol instead of a monster from across the rift, the team finds a man.  They bring him back to their base and discover he is a descendent of the force leader from World War I that not only repelled an earlier attempt at invasion, but had also disappeared.

The book starts out with a bang and moves along at a great pace.  The characters are developed quite well and I was very taken at how Craig was able to keep a number of distinct personalities together and work their interplay in an effective fashion where no individual seemed contrived or otherwise ineffective. 

My one qualm with the book was the occasional diversion away from saving the world for intimate interpersonal relationships.  I found this a bit distracting, wanting to get back to learn more about the monsters, the rift, the other world and whether or not the Earth would be saved.

I would recommend this book to anyone who enjoys classic science fiction or anyone who wants a fast paced read.

Overall I would give the book 7 out of 10 stars.