Mamatas is most known for his horror and dark fiction but claims broad influences. Writer
Laird Barron described the short fictions in
You Might Sleep... as running "the gamut of science fiction, fantasy, metafiction, horror, generic lit, to the realms of the effectively unclassifiable".
The Internet Review of Science Fiction, reviewing
You Might Sleep, contends that "
J.D. Salinger [is] an obvious but unacknowledged influence" and also compares Mamatas' work to "
Lewis Carroll with an
ISP, Mishima hammering out his
death poem on a
BlackBerry or
Harlan Ellison hyped up on
crystal meth..." while suggesting a certain immaturity to Mamatas's themes: "Despite his tremendous gifts, Mamatas dares little. One wonders how he would handle more profound materials, how his narrative sorcery might encompass (for example) bereavement, real tragedy or loss of self through enlightenment or love." A thematic touchstone for Mamatas is
H.P. Lovecraft. His novel
Move Under Ground, which combines Lovecraftian and
Beat themes, was declared one of the best
Cthulhu Mythos stories not written by Lovecraft by
Kenneth Hite in the book
Cthulhu 101. Mark Halcomb of the
Village Voice reviewed the book and its peculiar meshing of Lovecraft and
Kerouac, writing, in part, "In fact, Kerouac's 'bebop prosody' and the Cthulhu mythos dovetail nicely, and what seems at first like literary stunt-casting actually gives Mamatas room to recast the Beats' fall from grace in fanciful terms unhindered by their tricky psychology, the strictures of reality and realism—or lingering platitudes."
Publishers Weekly reviewed
Move Under Ground, discussing the novel's "credible pastiche" of Kerouac's voice and declared the book "sophisticated, progressive horror..." A number of his short works, such as the
novelette Real People Slash and the
flash fiction "And Then And Then And Then", also explicitly combine Lovecraftian themes with the voices of non-fantastical literature. The short story "That of Which We Speak When We Speak of the Unspeakable", first published in the anthology
Lovecraft Unbound is a pastiche of Lovecraft and several of the works of
Raymond Carver.
The Damned Highway combines a character based heavily on
Hunter S. Thompson and Lovecraftian themes. Satire is also a significant element of Mamatas's fiction.
Ed Park, writing for his online
The Los Angeles Times review column, described Mamatas's
Under My Roof—a short novel about the formation of a
microstate on
Long Island—as an "accurate, fast-moving satire that transcends mere target shooting by virtue of its narrator, Daniel’s 12-year-old son Herbie". A starred review in
Publishers Weekly for the same title also highlighted the satirical elements in the work, declaring: "A big-bang ending caps the fast-paced novel, and there's much fun to be had watching Mamatas...merrily skewer his targets." Mamatas's nonfiction work includes essays on
publishing,
digital culture, and politics. His
Village Voice piece on the
Otherkin phenomenon is cited as one of the earliest national publications on the subculture. His essay about his settlement with the
RIAA for
file-sharing has been cited in several
law reviews, as it is a relatively rare first-person account of the process of settlement with the RIAA. Essays from
The Smart Set,
Village Voice,
The Writer and
Tim Pratt's
fanzine Flytrap were compiled, along with original material, into the writing handbook
Starve Better in 2011, and published by
Apex Publications His essay "The Term Paper Artist" originally from
The Smart Set, about his experiences as an academic ghostwriter for pay, has been discussed on
National Public Radio and reprinted in a pair of textbooks, both published by
Nelson Education. ==Major works==