Okay, now without the hyperbole: Matthew Finch's Swords & Wizardry is an honest-to-goodness retro-clone of the original D&D rules from 1974-75--sometimes referred to as "0e". It's not an exact replica of the Little Brown Books, however, as it incorporates a few rules and developments that came after. S&W aims for a goal loftier than mere reproduction, anyway: the preservation of not just 0e's rules but its play style. S&W is a hobbyist's game.
"IMAGINE THE HELL OUT OF IT!"
To understand what that means, let's talk mechanics. Compared to the average modern game design, Swords & Wizardry's rules are pretty sparse. You get character creation and advancement, combat, magic rules, spells and a bunch of monsters. There are no skill lists, no comprehensive combat modifiers and certainly no feats; there's not even a task resolution system beyond that necessary for beating stuff up. And PCs have only one saving throw! So how do you get anything done?!
Enter the hobbyists' approach.
In true old-school fashion, the noticeable gaps are not an omission--they are implicit carte blanche to do whatever the hell you want for your players and your game. This requires creativity and effort on your part...hence, the 'hobby' concept. The result is refreshing, as you have a few basic rules to handle the essentials and free reign to dictate everything else.
THE MYTH OF HACK-AND-SLASH
In the act of being a 0e retro-clone, Swords & Wizardry exposes an often-overlooked aspect of the old game it's based on: a heavy role-playing element. With no diplomacy skill available, what are you going to do when it's time to talk your way out of trouble with the city guards? Well, the GM may call for an off-the-cuff die roll that somehow takes your Charisma stat into account...or he may just ask you to role-play your way out of it. That's why we call them "role-playing games", and have since 1974.
In fact, the superimposition of the players' creativity and imagination is arguably the key to making the game work as anything more than a skeletal collection of basic ideas. For instance, consider that S & W offers only three character classes--Wizard, Fighting Man and Cleric. By themselves, those classes describe a very basic concept (fighting men fight, wizards cast spells, etc.) and no more. By not fleshing these out for you, the game encourages you to define the character yourself. Is your Wizard really a cackling sorceress, or an insightful, sagely scholar, or perhaps a nobleman with magic in his or her veins? In S & W, the difference between a swashbuckling pirate, a grizzled veteran soldier and an energetic young barbarian is not one of game mechanics; it's one of character concept and its execution by the player.
THE OLD SCHOOL MEETS THE NEW
As mentioned above, S&W isn't an exact recreation of the 1974-75 rules. I haven't ever seen those rules, but I have it on good authority that variable weapon damage is not a feature from that edition, and S&W incorporates it. The game also includes a very modern option: ascending Armor Class. AC can go downward as it improves, or upward; GM's choice.
And what of demihumans? In character creation, players have the option of playing an elf or a dwarf, which are treated as classes unto themselves, but with a strong rationale to support the fact. The ideas are fairly clever, and make these seemingly restrictive options surprisingly flexible in play.
Any game is only as good as the experience you have with it. The quality of _Swords & Wizardry_ as a game experience is going to depend, ultimately, on the audience's approach to it. Simply stated, aims for a goal and hits it square on...but it may not be the itch that you need scratched, and there may be things about it that don't do a thing for you.
Gamers who don't want the hobby-game experienced are, obviously, cautioned; the make-it-up-as-you-need-it mindset is absolutely integral to playing this game. The lack of some classes (read that as "thieves") may bamboozle if not completely turn off some players; it is assumed that traditional "thief functions" (searching for and removing traps, climbing walls, moving silently, etc.) can be attempted by any character, and a GM who doesn't prepare room- and trap descriptions ahead of time will be at a loss to run the game this way. Some folks may balk at the low amount of hit points that Fighters get. Strokes and folks, after all.
You can get this game for free, so the price is right. The approach is refreshing and the love and care put into the project is obvious. You can't lose if all you do is check it out; indeed, you might find a new favorite game.