Whether the goal is to resist the pernicious rise of a new edition (see also: "D&D 4 sucks because it's like tabletop WoW!"*), to evoke the memories of one's youth (see also: "I've never enjoyed any game as much as second edition AD&D...") or to produce something mechanically recognisable that wears its influences on its shoulder but isn't coasting on the nostalgia factor (see also... ummm...), retrocloning is a part of the roleplaying world now.
I'm not here to give a potted history of the retroclone, because I'm not a D&D archivist and I'm bound to get it wrong, but to poke and prod at the concept itself. Retrocloning fascinates me, you see. Not being old enough to have played the Original Game - I came in at the tail end of AD&D second edition - I'm curious about this strange, hoary artifact which, despite not being especially well written, or organised, or presented, ensnared the hearts and minds of millions for a while.
Insofar as I can work out, the idea of the retroclone is to take the essential mechanics and spirit of one's preferred roleplaying experience, run them through the editorial wringer a few times, bolt on one's favoured house rules, and then release same as a self-contained RPG in its own right. It's generally done for the earliest editions of D&D, though there is of course the small matter of Pathfinder (which derives from the windy, bloated, quite-elegant-at-its-core-shame-they-didn't-know-when-to-STOP Third-And-One-Half edition, but which is shaped by the same principle - the refusal to put down something you like just because the 'official' variant has changed).
Critics of the retroclone are swift to point out that this is often an exercise in copying, pasting and selling the works of others to a niche market that still has echoes of the gift economy about it, and will consequently feel obliged to buy any old guff if it looks like Russ Nicholson did the cover art. This is not an inaccurate observation, I feel; the essential business of cloning an earlier edition of one's favourite RPG is the sort of thing which only really needs to be done once. I don't think the world needs OSRIC and Labryinth Lord and Lamentations of the Flame Princess and Swords and Wizardry and argh. Nope.
In terms of gameable, a lot of these are... very similar concepts. The devil's in the details, as one might expect - personally, I quite like Lamentation's upgrade to a Renaissance setting, drift away from conventional 'monsters', arcane summoning mechanics and focus on 'gentleman adventurers' who have the independent means required to pursue shenanigans like these. I also quite like Swords and Wizardry's options for a second-edition style pseudo-THAC0 hit system, or a third-edition style armour-changes-how-high-you-need-to-roll one. I also quite like... you get the idea, I'm sure. There are good ideas scattered all over these things, but each is embedded in a self-contained product, and I can't help but feel that if the OSR didn't keep reinventing the wheel, it could be doing something significantly more useful than copying-and-pasting the AD&D or OD&D rules again.
What I'd like to see instead is modules - good ones, mind you, none of that "this room contains d6 rats and d100 copper piece" malarkey, I can invent boring rooms all day long, you know- and above all setting books. Dungeon Master's Guides. Volumes which tell me how to run a game like yours, what alterations you've made to the core rules and why. Exemplary materials, not yet another self-contained RPG distinct from all others but demonstrations of fantastic imagination and inventiveness.
I'm not saying that major alterations shouldn't be made to one's preferred rules system in order to achieve one's goals (I am, after all, the Disintegrator GM around here), but why bother copy-pasting the rest? State your core system of choice, state alterations with brief justification (friends don't let friends write like White Wolf developers), demonstrate through example materials (NPCs, encounters, short adventure paths, dungeon environments - samples of playable content!) how your setting works, chuck in a reading list, but don't waste your time and mine on telling me, yet again, how a Fighting Man works and how much his bardiche costs.
And for anyone who's wondering about me putting my money where my mouth is; I'll be doing it the second I decide what kind of D&D I want to run.
ETA: I'd like it noted that I'm not ignoring the comments, especially not just because they disagree with me. I love being disagreed with. What I don't love is Disqus (and IntenseDebate) both deciding to lock me out and trap me in endless login loops. If anyone has a suggestion to resolve this, leave it in the comments - pat on the back from me if it works!
* - which is ironic, to me, since the bits of World of Warcraft which vex me most are... the most D&D-ish bits - random loot tables, obligatory 'fantasy' races etc. etc.