Grunts!

Halfling hand job. Turgid orc dicks.

Also, machine guns and castle raids and shit.

If that doesn’t sell you on this book, nothing will.

As I try to plow through the oldest books on my "to-read" shelf, I realize that whatever intuition it was that kept me away from these books for so long, it was a sound one. This story seems to be driven entirely by the author's premise (as described in her introduction) of orcs in a fantasy setting wielding Vietnam-era firepower and talking like characters from "Full Metal Jacket," and she fleshes the story out beyond that using a series of buffoonish fantasy characters and familiar-sounding conflicts seen from the orcs' perspective. Don't ask me how the orcs learned to talk like that or came to identify themselves as "Orc Marines," that happens outside the narrative and no explanation is given. Maybe that's for a future book, but I could only manage a quarter of the way through this one, even skimming.

Not as out of character as you may think given MG's fascination with mediaeval warfare, Grunts! was inspired by a late-night drinking session with Neil Gaiman, er, the pleasant concept of a crossover between Tolkien's orcs and the Vietnam War, at least as depicted in popular film.
Basically, a dragon capable of transdimensional hoard-accumulation has accumulated a stash of US Marines materiel and guarded its hoard with the curse 'You are what you wear.' Cue a troop of Orcs led by the fearsome Ashnak who come and raid the place. Cue some very amusing hi-jinks which unfortunately (markdown for this possibly) do not really get jolted out of the joky style even (for example) when our anti-heroes attack a provisions train and if there was a Geneva Convention, well, they'd break it so bad it might as well never have existed. That might put people off, at least nowadays.