The year is 1898. The great detective, Sherlock Holmes, is presumed dead; and enemies of the crown are gathering at every turn. To counteract the threat, British intelligence recruits five unlikely individuals to form an elite group of agents. They are: Hawley Griffin, best described as The Invisible Man; Dr. Henry Jekyll, whose strange case also involves a certain Edward Hyde; Captain Nemo, whose submarine vessel, the Nautilus, travels 20,000 Leagues Under the Sea; Allan Quatermain, famous for exploring King Solomon's Mines; and Wilhelmina Murray, who had a scandalous involvement with a late foreign nobleman named Dracula.
The League of Extraordinary Gentlemen is basically a steampunk/superhero comic, starring characters culled from notable literature of the Victorian era. Apart from the five main characters (well, six, if you count Jekyll and Hyde as two characters), there are extensive guest appearances and cameos from a host of other literary works ranging from the famous (Edgar Allan Poe, Charles Dickens, Lewis Caroll) to the painfully obscure.
Apart from these references, a great deal of the fun of the series comes from how they play up the Victorian setting, complete with stuffy dialogue and delightfully ironic displays of sexist/racist/imperialist attitudes of that era. There are scenes of gratuitous violence and sexual allusions, which the editor proclaims as "exciting to the manly, outwardgoing youngster of today", while simultaneously cautioning lady readers against them. To round it out, every issue contains several pages of bizarre Victorian advetisements (both authentic and not-so-authentic), and a hilariously pompous and condescending Letters to the Editor column.
The comic is written by the distinguished Mr. Alan Moore, of Watchmen and From Hell fame, with art by Mr. Kevin O'Neill. Unlike some of Mr. Moore's previous works, LoEG is not amazingly deep or thought-provoking. What it is is action-packed, engaging, and terribly clever, with well-defined characters.
For those who are unfamiliar or only marginally familiar with the series, this site can hopefully provide some basic information. For established fans who've read every issue, I don't have anything nearly as useful as Jess Nevins' annotations for the series; but you might enjoy some of our pointless amusements anyway.