Chris Jones over at Classic RPG Realms writes how D&D and AD&D were two different games. Looking around at what I’ve heard and seen of 5e (no, have not played it), what I’d played of the original basic (mostly Keep on the Borderlands) and AD&D (a fair bit including some heavy home-ruling) and Pathfinder, I think he has a point that other games evolved more from original D&D. I think AD&D evolved from the other more than he believes, it needs some distilling, but even ACKs, which I dearly love, owes more to Basic D&D than AD&D, and most OSR games do as well.

One thing that jumped out at me was the following:

Now, this may seem simple to some. Maybe others have experienced the same thing in other games. Even games based on Original D&D. I have not. In fact I am struggling with 5e now for this very reason. The game seems shallow, and lacking in substance. I feel like it is the copy of a copy of a copy. And yes, very cartoon-like. This has been something I have struggled since I came back playing 3.5. I see them as very cartoonish and over the top. Not the fantasy I like to imagine. I also feel it is far too oversimplified, even the massive 3.5, 4e, and PF. Yes, even these huge option heavy systems where the complexity is in the proliferation of character options instead of actual game depth. The exact plagues that Gary mentioned before are the very ones that have plagued D&D since its inception–those that AD&D was supposed to rectify.

Insofar as PF that criticism is spot on. Lots of tour books (inner sea guide, this guide, that guide), and book, after book, after book of character options where a number of people who regularly play refuse to make up characters by hand to track all the options, but instead use Hero Lab.
Yeah, AD&D could get complicated, but the Players Handbook was the players handbook, and the DMG was the DMG, and you didn’t end up with “Ultimate this” and “Ultimate that” and the other thing..
Reading this article it occurred to me that as thick as the PF core rules book was, it spent far too much of its space on characters.
The first 17 pages are “how to play RPG’s” of which the last few are an overview of the character generation process. Chapter 2 – 10 pages or so – delves into stats and fluff on each of the races, in fine print. Classes ties up the next 56 pages (and keep in mind that there are a lot more books with even *more* classes, this is just the core rules…). Another 50 pages on skills and feats. 
With the exception of combat and additional rules, you don’t *really* hit the GM-specific rules until page 394. Of those first 394 pages, 330 are basically the players handbook (though you could argue a good chunk of equipment belongs in the DMG…)
This in a book with 575 pages, in a system which has several bestiaries, an advanced players guide, and far more beyond that for character options that I haven’t even begun to cover.
Let’s compare this to ACKs. 270 pages for the core rulebook. 14 to introduce the game and its tone. 76 more pages to cover basic character classes, equipment, proficiencies, and spells.
All the rest is GM stuff.
Is ACKs the successor to AD&D? No. As set forth in the article, it very much is rooted in the original D&D. 
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It to me strikes a perfect balance between simple enough and complicated enough. A chunk of the GM section is consolidated economics and rules of thumb so that when your character (or his “heir” several deaths later) becomes powerful enough, you actually have the framework needed to get a castle, a kingdom, a town, and so forth built – something even AD&D didn’t manage, and D&D didn’t even try. It fleshed out the world to fill in holes in basic D&D (and as noted, even AD&D), while at the same time making the rules a little more consistent.
This last is where the genius creeps in. Alexander Macris saw the original rules and the potential in them, and tweaked them so that they could easily be extended up to clashing armies (Domains at War) and basic firearms (Guns of War) of the pike and shot age. The classes in the core book are closer to the original D&D than AD&D, but they’re based off the methodology in the Players Companion, giving you both ready-made templates with few – but significant – options to choose, and a very flexible character creation system that distills down to a simple character sheet that works.
And soon, they will publish another adaptation of the rules for heroic fantasy.
While, in my youth, I leapt to AD&D and never looked back, I agree that something was lost in the quest for completeness, and consistency. If I had to chose between my childhood systems of D&D it would be AD&D in a heartbeat.
That said, I’m not sure that, at least as shown in ACKs, going back to the same roots hasn’t resulted in at least *some* better stuff. Yes, Pathfinder has certainly worn on me with its bloat and shallow breadth, but the additions to ACKS actually change the nature and depth and core rules of the game – yet you can take them or leave them as you wish.
We have at least one system that manages the complexity, reasonable conceptual consistency, and verisimilitude that AD&D aimed for, but slightly leaner, and giving the GM more room to decide what actually makes sense in the light of what the players decide.