I played in a rather odd RPG at Go Play NW. It's a third-party version of the original, three-book D&D rules set. There are apparently several such innovations. Castles & Crusades might be the best known. We played Swords & Wizardy. I rolled up an elf and adventured through a dungeon. The DM was Wilhelm Fitzpatrick, the Dragonflight events manager.
The game has a lot of warts, but it played really fast. Combat was arbitrary but it was blessedly fast. We didn't use miniatures. That's a break with tradition, but it seems to represent a bald refusal to be realistic and or attempt simulation. The interesting thing is that we can now approach the original D&D rules knowing everything we know about game design and role playing. Used judiciously, the system works and is simple, just what you need for a more story-oriented game. I think there are some interesting possibilities along these lines.
The problem with such games is that there's a lot of bad stuff that people are nostalgic for. For every bad rule that you might want to strip out, there are people who won't think your OD&D is original enough if you don't have it. Swords & Wizardry even has two AC systems that it uses side-by-side: the old-fashioned 9-down system that they have to include for tradition's sake and the 10+ system that they have to include because it's just clearly better.
Swords & Wizardry free PDF:
http://www.rpgnow.com/product_info.php?products_id=62346 Another version is Labyrinth Lord: (
http://www.rpgnow.com/product_info.php?products_id=29547&it=1)
Microlite74: (
http://www.retroroleplaying.com/content/microlite74) (added 5 July)
For the 1E version, there's OSRIC (
http://www.yourgamesnow.com/index.php?main_page=product_info&products_id=362)
And for Gamma World fans: Mutant Future (
http://www.rpgnow.com/product_info.php?products_id=56282)
Added 5 July 09: For the record, the "bad stuff" I'm referring to is stuff like: too much arithmetic (5% XP bonus, copper pieces, etc.), wonky XP progression per class, too-random character creation, and poor class balance. It also has the problem that didn't get fixed until 4e: all spells are daily, which makes spellcasters play too differently from the fighters.