Part 3 of his series really dives into what the OGL is. Here's the opening paragraph.
WotC introduced the OGL and the System Reference Document 5.0 (“SRD5”) for the noble cause of telling the public which of the material they published was, in their opinion, protected work (i.e., work only they could publish), and which was public domain (i.e., freely useable by everyone without restriction). This isn’t sarcasm; their stated intent was noble. Sure, they called it a license when it clearly isn’t, but if that were their only sin, we could all overlook that. The idea was to avoid as many unnecessary disputes as possible. That’s helpful. It has since morphed into an oxymoronic attempt to license public domain material and intimidate members of the industry and community in general, who are fearful, ignorant, or unable to finance a defense against a lawsuit. That’s damaging.
https://gsllcblog.com/2019/08/26/part3ogl/
EDIT:
What Exactly is Licensed by the OGL?
Open Gaming Content is the content WotC says the public can use, and Product Identity is the content WotC claims the public can’t, but Open Gaming Content can’t be copyrighted because it’s already in the public domain. By its own terms, the
5th edition Dungeons & Dragons OGL (“OGL”) grants to gamers something that the gamers already have the right to use. Thus, no consideration passes to the gamers, and the OGL is a legally null document.
The OGL defines two gaming elements: The “Open Game Content” and the “Product Identity.” Open Game Content (“OGC”) is defined in paragraph 1(d) as
“the game mechanic and includes the methods, procedures, processes and routines to the extent such content does not embody the Product Identity and is an enhancement over the prior art and any additional content clearly identified as Open Game Content by the Contributor, and means any work covered by this License, including translations and derivative works under copyright law, but specifically excludes Product Identity.”
Next is the Product Identity (“PI”). In summary, paragraph 1(e) gives a comprehensive list of everything relevant to the RPG that could possibly be protected under copyright or trademark law and defines that as PI. For the sake of argument, we’ll assume that, except for game mechanics or items specifically excepted below, anything WotC has historically claimed to be copyrighted or trademarked material is indeed protected.
Let’s break down OGC first. It includes the game rules (a.k.a., “game mechanics”), which are not copyrightable, so everyone may distribute them without restriction. The definition goes on to point out that if any game rules are copyrightable, then they’re included in Product Identity. Technically, this is correct, but there are no game rules in PI (as a matter of law), so nothing is transferred into that pool of material. The talk about copyright law in this term is without substance. This means that the OGC is subject matter a gamer may use without WotC’s permission, and thus doesn’t require a license. Compare that to PI, which is everything gamers can’t use unless they have a license from WotC, and we get to the crux of the problem. Turning to paragraph 4:
“Grant and Consideration: In consideration for agreeing to use this License, the Contributors grant You a perpetual, worldwide, royalty-free, nonexclusive license with the exact terms of this License to Use, the Open Game Content.”
In plain English, “We’re licensing to you game mechanics, which we have no right to prevent you from using.” Now paragraph 7:
“You agree not to Use any Product Identity, including as an indication as to compatibility, except as expressly licensed in another, independent Agreement with the owner of each element of that Product Identity.”
In plain English, “We’re not licensing anything that we
could theoretically license to you, so you may not use Product Identity. In fact, you can’t even say that your original work is compatible with our game system.”
Ergo, WotC is licensing nothing with the OGL. They claim to license something they have no right to license (OGC), and anything that requires such a license is explicitly excluded (PI). Moreover, they don’t even want third parties to mention their game system. Once again, in plain English: “We’re licensing to you what we have no right to claim as ours, and not licensing you anything we can claim as ours, and are thus giving you nothing.” Even if a third party signed this agreement (probably no one has; there’s no signature line), or if a court bound the third party to its terms because it was printed in a book as instructed in paragraph 10 (“You MUST include a copy of this License with every copy of the Open Game Content You Distribute.”),
there’s no consideration, so there’s no legally enforceable agreement.