Swords and Wizardry is a cleaned up OD&D. Initiative makes sense, attack bonuses and armour class ascend, and saving throws are unified,

Labyrinth Lord seems to be a popular choice around here, but I honestly don't know enough to differentiate them, they all look the same to me.

I like the ones that aren't so "cloney."

I guess I should say I like OSR games better than retro-clone games.

ACKS is a simulacrum (versus a retroclone) of the Moldvay/Cook Basic/Expert DnD basic rules. So, you have things like Elves and dwarves as a class, the max level is 14, and other stuff like that. However, it's not a retroclone (by which I mean it's not purely trying to recreate the old system) but rather uses that as a jumping off point. So we have two new race classes (an elven assassin/mage, and a dwarven craft-priest) and a handful of new classes for humans as well (Bards, Assassins, Explorers, and Bladedancers). In the Player's Companion (a book they did a Kickstarter for asking for $4K and they have already raised 15.5K for) there are rules for creating your own classes as well as two new races. Combat also has more depth, allowing you to do maneuvers from disarming opponents to sundering their weapons to grappling them, all in a quick and easy add on to a combat system that already flies compared to later iterations of dnd. And there are the Proficiency rules which are kind of like a mixture of skills and feats from other systems (so if you want to play a fighter who can sneak like a thief, you can do that, or a Wizard who is also a Siege Engineer). And of course it has a huge section on becoming a Conqueror and a King wherein you rule your Domain and spread it until you could possibly rule an empire. They are even working on a Mass Combat system that plugs into it for waging your wars.

While I've been nostalgic about the old days and the beginning of my old campaign (which started in 2nd ed) I've not been able to be pulled back into those systems because, while I can see the appeal, they are just too mechanically simplistic to hold my interest. I guess I need characters that are mechanically different in meaningful ways. This system has hit my sweet spot... Proficiencies allow for special abilities and skills, the combat system has depth well beyond any of the earlier dnd combat systems, and with the class creation system, I can make most archtypes fairly easily.

Oh, and they handle the yo-yo of hit points in a way that is nice and realistic (if you drop below 0, you don't know what happened to your PC until another character examines you... there is a chart that you roll on (with various modifiers based on how quickly they check you, how low your HP are, whether they use magic to heal you, etc) and based on what you roll you could either be dead, or crippled or suffering a serious permanent wound, or just need a few weeks bed rest... but you aren't just going back into the fight. They have a similar chart for Raise Dead... it's so easy to come back...wrong. The designer said they lost more high level PCs to retirement or suicide because they were so broken or monstrous from having been brought back to life they couldn't cope.

So basically, it fixes a lot of my quibbles with DnD, while catering to the things I liked (even some of the things I thought I didn't like anymore but find that I do).