My preference for a 50th anniversary edition would have been a tidied up AD&D.
To me that describes
Adventures Dark and Deep.
"Well,
that's because Adventures Dark & Deep isn't quite a retro-clone. Almost, but not quite.
Adventures Dark & Deep (abbreviated ADD) bills itself as being "based on Gary Gygax's plans for expanding the game." So it's claims to be a clone of neither 1st or 2nd edition AD&D. Instead it is a spiritual successor to AD&D 1st edition, with a distinctly Gygaxian design. Constructed by Joseph Bloch from notes, articles and blog posts by Gary Gygax it claims to be written as what the author believes AD&D 2nd edition might have been if the game's original creator had not parted ways with TSR some time before the release of second edition."
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The book works under the premise of what would 2nd Edition have looked like if Gary Gygax had stayed at TSR. Joe has taken articles, interviews and discussions and something like an anthropologist pieced it all together to get something new and yet familiar. Unlike the previous book, the Player Manual makes no assumptions that you have AD&D1 or OSRIC. There are some obvious roots in those games, but this is now it's own thing."
"The book does capture the feel of old D&D with some interesting twists. None that would trip you up, but still enough to make you go "huh, that is kind of neat"."
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ADD is, if nothing else, a clone of AD&D 1e with lots of new options and classes. It reads much like 1e to me just more user friendly, which is a compliment. ADD cleans up much of what was broken in Unearthed Arcana (sometimes known as AD&D 1.5) and fixes it.
Much of the draw of Adventures Dark and Deep are the new character classes, which can be easily dropped into any AD&D 1e / OSRIC campaign with little effort. I’ve always felt an affinity to Bards, and Joseph Bloch has an excellent version included. The Jester subclass reminds me of the old NPC class from Dragon Magazine - I remember my sister playing one."
"So: what to say about ADD? Imagine you had collected for an OSR game a rule-set of AD&D that included everything Gary Gygax ever wrote about the game, all the crazy stuff he put in Unearthed Arcana, stuff he put in Dragon, stuff he shared in private thoughts, stuff elaborated from vague ideas about how to remake the AD&D game, just packing as much stuff as Gary Gygax possibly could. Now imagine its not Gary Gygax at all, and just some guy named Joseph Bloch."
"What we get from ADD is a VERY complete Old-school RPG; I'd dare to say that it is truly more complete a game than AD&D 1e itself. Out of all the various old-school editions, it is most similar to AD&D 1e, since it uses it as its starting point; I'd go as far as to say that more specifically, you'd particularly like this game if you're a big fan of playing AD&D with Unearthed Arcana and with all kinds of weird ideas culled from old Dragon magazines. What you get in it, in fact, is a very odd variant of 1e with some unusual modifications, enough that it would certainly feel like quite a different game (while still being very recognizably old-school)."