I've been looking over the various “retro-clone” RPGs that use the Open Game License to re-vision classic versions of D&D. Some of them are pretty darn good. Better than the original in many ways. But none of them, so far, have hit the absolute sweet spot I'm looking for.
Swords & Wizardry looks fantastic. Great layout and art, nice clear writing. Lots of modular options for including or excluding certain rules. It has a good list of classes that includes the monk and assassin. I love the single saving throw rule. Instead of the original list of saving throws or the SRD v3.5's list of three saving throws it just has one. It uses the old descending armor class method by default, but includes the ascending method in parenthesis if you want to use it. So an AC might be listed as 9[10] or 5[14]. I personally can't stand “to hit” tables so I like the ascending method best.
Basic Fantasy RPG also looks great. The layout and font choice is extremely reminiscent of my favorite D&D set: the Moldvay/Cook/Mentzer or “B/X”. If I wasn't such a fan of ascending AC and fewer saving throws I'd still be playing B/X. However, BFRPG really does a bang up job of capturing the old vibe while embracing some of the new. For example, it uses ascending AC without any silly to-hit tables. Characters get an attack bonus as they level up. I can't understand why anybody would cling to the older method using tables to figure out what you need to roll. Just roll, add your bonus, and compare it to the damn AC. Simple.
The only problem I see with BFRPG is the use of the older style of saving throws. But hey, I like that better than to-hit tables. And this is a free game that offers the core content in a very simple, usable format. It would be really easy to create content for this game.
I have not yet examined Labyrinth Lord. This one seems to be the darling of the retro-clones, claiming quite a large fan base. From what I understand, LL is a Moldvay clone...so maybe I will fall in love with it.
OSRIC is another one I haven't really dived into. It is a 1st edition clone all the way. And again, totally free.
Other games are out there too that go down this path to some degree. A game I fell in love with and purchased is Dungeon Crawl Classics RPG. The massive 480 page tome is now a prized possession of mine (wicked wizard cover). I've ran the game a few times and I love it's simplicity. The heart of DCC is just a really stripped down D&D with old school vibe and more modern mechanics. No to-hit charts, ascending AC is used, the core mechanic of d20, and it has 3 saving throws (Fort, Ref, Will). It has no Feats or Powers! I do love that about it. The bulk of those 480 pages are taken up by spell charts and killer artwork (Jeff Dee, Roslof, and many more). The magic system is crazy and has a ton of randomness built into it. I'm looking forward to running the game for some players that choose to be wizards...just to see what will happen.
But I'm kinda thinking of writing my own personal version of these beloved old rules. If I do, it will be a 64-page book. No more, no less. It will use ascending AC with no to-hit tables. It will use a simplified saving throw method, possibly the 3 saves from the SRD v3.5. And it will use the core mechanic for almost everything. Hey, I'm a simple kind of guy.