Both the characters and the language are truly an immense joy to discover; they're completely fantastic, even if they have quite a bit of variance from one story to another (not a bad thing; kind of like what people say about the Beatles, you can see Leiber evolving and experimenting with his art form, not just churning out longer hack-work over time). It probably doesn't hurt that Leiber based the characters on real-life models, namely himself and his friend Harry Otto Fischer.
I've written about one of these stories previously, in the context of D&D thieves-reading-magic-scrolls. But I really started with Fafhrd & the Gray Mouser about a year ago with the comic collection by Howard Chaykin and Mike Mignola -- comic artists I admire greatly -- which frankly left me a little cold. The action seemed random, unpredictable, and unmotivated. Fortunately, there is a short 10-page preview of the original text at the back, which itself I found to be electrifying. The answer to this riddle is the immensely strong narrator's voice used by Leiber, with all its flourishes of language, cosmic description, and internal monologues and conflicting desires; much like a movie based on similar books, any adaptation can't avoid losing the essence of the thing, namely the amazing richness of the written word.
Here are a few sections that struck me as particularly memorable from the brilliant, if relatively down-tempo, 1968 short story "The Wrong Branch" (which on the prior point, has almost no spoken dialogue at all). It starts with this:
It is rumored by the wise-brained rats which burrow the citied earth and by the knowledgeable cats that stalk its shadows and by the sagacious bats that wing its night and by the sapient zats which soar through airless space, slanting their metal wings to winds of light, that those two swordsmen and blood-brothers, Fafhrd and the Gray Mouser, have adventured not only in the World of Nehwon with its great empire of Lankhmar, but also in many other worlds and times and dimensions, arriving at these through certain secret doors far inside the mazy caverns of Ningauble of the Seven Eyes -- whose great cave, in this sense, exists simultaneously in many worlds and times. It is a Door, while Ningauble glibly speaks the languages of many worlds and universes, loving the gossip of all times and places.
And then, during a danger-filled sea voyage:
Near Kvarch Nar they did manage to reprovision, though only with coarse food and muddy river water. Shortly thereafter the seams of the Black Treasurer were badly strained and two opened by glancing collision with an underwater reef which never should have been where it was. The only possible point where they could careen and mend their ship was the tiny beach on the southwest side of the Dragon Rocks, and it took them two days of nip-and-tuck sailing and bailing to get them there with deck above water. Whereupon while one patched or napped, the other must stand guard against inquisitive two- and three-headed dragons and even an occasional monocephalic. When they got a cauldron of pitch seething for final repairs, the dragons all deserted them, put off by the black stuff's stink -- a circumstance which irked rather than pleased the two adventurers, since they hadn't had the wit to keep a pot of pitch a-boil from the start. (They were most touchy and thin-skinned now from their long run of ill fortune.)
As they were anchoring in Ilthmar harbor, the Black Treasurer literally fell apart like a joke-box, starboard side parting from larboard like two quarters of a split melon, while the mast and cabin, weighted by the keel, sank speedily as a rock.
Fafhrd and Mouser saved only the clothes they were in, their swords, dirk, and ax. And it was well they hung onto the latter, for while swimming ashore they were attacked by a school of sharks, and each man had to defend himself and comrade while swimming encumbered. Ilthmarts lining the quays and moles cheered the heroes and the sharks impartially, or rather as to how they had laid their money, the odds being mostly three-to-one against both heroes surviving, with various shorter odds on the big man, the little man, or one or the other turning the trick.
Ilthmarts are a somewhat heartless people and much given to gambling. Besides, they welcome sharks into their harbor, since it makes for an easy way of disposing of common criminals, robbed and drunken strangers, slaves grown senile or otherwise useless, and also assures that the shark-god's chosen victims will always be spectacularly received.
When Fafhrd and the Mouser finally staggered ashore panting, they were cheered by such Ilthmarts as had won money on them. A larger number were busy booing the sharks.
One thing is that Fafhrd & the Gray Mouser stories are the most pitch-perfect representations of D&D play that I've ever encountered; turned around, you could easily argue that D&D itself is basically a simulation of the rogues-from-Lankhmar stories. They are venal, bold and aggressive, sanguine and insouciant in the face of the greatest wonders and outrages, bonded as a team unquestioningly even with a background patter of ongoing, casual dispute.
Another thing that happened is that I adored the language and tone so much that I started reading passages, such as those above, aloud to my lovely girlfriend Isabelle. I completely hadn't noticed it previously, but her observation was that listening to the Gray Mouser was practically identical to just hearing me talk normally (incessantly skeptical, technical-minded, kind of cranky, etc.), and that conversations between the two of them had the exact tone of many of our own ("It's us!", she exclaimed). Apparently I'm being called "Gray Mouser" around here now, for at least a few days.
It's really a wonderful body of work. In particular, the novelette "Stardock" may be the single most perfect, fully-formed and satisfying fantasy adventure story that I've ever read. It's like a perfect little gem (ironically). Highest recommendation.