Shakespeare had the ghost of Hamlet's murdered father appear to reveal his killer. Mr. Kafka starts a story with a dude named Gregor waking up to discover he's
metamorphosized into a giant bug. And, more recently, Alice Sebold narrated
an entire novel from the point of view of a murdered 14-year-old girl hanging out in heaven.
Literary gimmicks such as these are one of the highest risk/highest reward tricks in literature. If done right, the writer is hailed as a creative genius and and his/her work as groundbreaking. Done wrong, and the writer is marginalized as, well, gimmicky — in the most negative connotation of the term.

Genre fiction (including fantasy) aside, let's define a literary gimmick broadly as something that could only happen (or be done) in fiction. Of course, this definition must come with the understanding that individual metaphysical and/or religious beliefs may drastically widen or narrow what's fictional and what's not. For instance, do you believe in ghosts? How about an alien named Xenu? Most of the literary gimmicks that work well, though, everyone will agree could not possibly occur in nature — and that's what makes them fun. For instance,
The Book Thief, by Markus Zusak, which I'm about a third of the way through, is an entire novel narrated by a gentle Death, who hates the human notion of him as a dark-hooded, sickle-wielding maniac.
Opinions on whether a literary gimmick works will, of course, vary widely by reader. For strictly literal-minded readers, literary gimmicks
are fantasy novels, and so will never be to their taste. For me, a gimmick works if it's clear why the writer made that choice — if it's a fundamental part of the way the novel must be told, and not just a writer showing off his/her supposed prowess.
I can't wait to hear from you about what gimmick-enhanced novels you've loved (or ones you've hated) and why or why not those gimmicks works. But first, here are a few that I've really enjoyed:

1)
Ishmael, by Daniel Quinn: A conversation between a man and a talking gorilla named Ishmael explores the relationship between humans and nature. Many fans (me included!) of this philosophical "novel of ideas" credit it as a logical foundation for the environmental movement. Man is made for the Earth, not the Earth for man, the book argues.
2)
Infinite Jest, by David Foster Wallace: The trick here is a film called
Infinite Jest that is so entertaining that those who watch it literally cannot stop. And so they die. This gimmick as well as the alternate reality future America (where years aren't numbered, they're sponsored — Year of the Trial-Size Dove Bar, e.g.) in which the novel is set provide a medium for Wallace to explore addiction in two separate ways: The traditional (drug and alcohol) and the more complex (our silly consumeristic, entertainment-driven culture). This brilliant 1,079-page behemoth is one of my favorite novels of all time.
3)
The Time Traveler's Wife, by Audrey Niffenegger: You know this one by now — time-traveling Chicagoan Henry jumps back and forth through the various stages of his eventual lover, Clare's, life. It's one of the most imaginative and touching love stories you'll ever read.

4)
House of Leaves, by Mark Danielewski: This multi-layered, mind-blowing piece of postmodern meta-fiction has as its cornerstone a house that measures larger on the inside than the outside. Characters get trapped in an infinite labyrinth, the door to which is inside this house. These gimmicks and a documentary film-within-a-story give Danielewski a jumping off point for exploring the existential question of whether the world is just a construct of the mind. This book requires a lot of work, but is easily the coolest, hippest and most innovative book I've ever read.
Now it's your turn: What are some of your favorite literary gimmick novels? What was the gimmick and why did it work? Alternatively (and perhaps more interestingly), what are some literary gimmick novels that didn't work?