As far as the design aesthetic this is pretty much what I was expecting and is pretty inline with del Toro and the artists we know he hired to do kaiju designs. Some people have cited the fantasy monsters from Pan's Labyrinth and Hellboy II, but those were as its been said fantasy creatures while with the PacRim kaiju del Toro seems to be going for a more sci-fi feel.
In many ways the kaiju remind me a great deal of Sammuel from the first Hellboy movie.

Interestingly talking about the more fantastical approach many Japanese artists take to designing kaiju, del Toro originally hired Japanese artist Yasushi Niraswa (Kamen Rider Kabuto, Den-O, GARO, Godzilla: Final Wars) to design Sammuel (and Abe) for Hellboy and his version had purple and red fur, piercings and sawed off horns with runes on them - and was rejected as being "too radical."