@Snarf Zagyg: Ok, so had some free time to review the historical elements and essays from OARs 1-6. Below is how I would rank them in terms of the historical content (versus the adventures).
The historical content generally falls into four categories: 1) Essays by ex-TSR employees, Goodman Games employees, and other affiliates recounting their glory days and personal experiences with the module (“Grognard”), 2) Essays on some of the backstory/history of the module (“History”), 3) interviews with ex-TSR employees (“Interview”), and 4) scans of some of the original printings (“Scan”). For me, I find the interviews tend to be the best parts, but the historical essays can be quite good (the one in OAR 6 really stands out).
1.
OAR 6 (Temple of Elemental Evil): Essays by Brendon LaSalle (Grognard), James Maliszewski (Grognard), Jon Peterson (History), Harley Stroh (Grognard/History), and Steve Chenault (Grognard). Interview with Jeff Easley. Scan of third printing of T1 (monochrome), scan of the cover of the seventh printing of T1 (full color), and scan of the third printing of T1-T4.
Comment: The historic pieces of this OAR tick all the boxes for me. The Jon Peterson piece in particular stands out as it includes original sketches from Gary Gygax. The interview with Jeff Easley is pretty good too.
2.
OAR 1 (In Search of the Unknown AND Keep on the Borderlands): Essays by Luke Gygax (OG Grogranrd/History), Mike Mearls (Grognard/Game Design Context), Harley Stroh (Grognard), Brendon LaSalle (Grognard), and Alex Kammer (Grognard). Interview with Mike Carr. Scans of the second and sixth printings of B1. Scans of the second and fourth printings of B2.
Comments: Set the standard format for future OAR’s. Interview with Mike Carr and essay by Luke Gygax stand out.
3.
OAR 2 (Isle of Dread): Essays by Zeb Cooke (Original Co-Author/History), Paul Reich III (Grognard), Lawrence Schick (Grognard/Known World History), Michael Curtis (Grognard), and Harley Stroh (Grognard). Interview with Zeb Cook. Scans of the first and fourth printings of X1.
Comments: Interview with Zeb Cook and essay by Lawrence Schick stand out.
4.
OAR 3 (Expedition to the Barrier Peaks): Essays by Michael Curtis (Grognard), Tony DiTerlizzi (Author/Illistrator/Grognard), Earl Otis (OG Artist/Art Process), and James Maliszweski (Grognard). Interview with Diesel LaForce. Scans of the first and second printings of S1. Also includes an essay by Jon Peterson on the tie ins to Metamorphosis Alpha in one of the appendices.
Comments: The Earl Otis piece stands out where he demonstrates the process of painting the Froghemoth. The Jon Peterson essay at the end is also interesting. Side note: the printing I have of OAR 3 was printed on glossy paper instead of the thicker stander stock used in the other OARs (not sure if that changed with subsequent printings). While this is great for the artwork, its less than ideal for reading the text and flipping pages.
5.
OAR 5 (Castle Amber): Three essays by Michael Curtis (two Grognard, and another focusing on the author Clark Ashton Smith, whose stories influenced the adventure), two by James Maliszewski (one Grognard, the other on Historical sources for the original adventure), Tim Wadzinski (Grognard), and Doug Kovacs (regarding the art he produced for the interior cover). Scan of the first printing of X2.
Comments: The essays on Clark Ashton Smith and the fictional sources for Castle Amber are good.
6.
OAR 4 (The Lost City): Essays by Chris Doyle (Grognard), Mike Mearls (Grognard/Adventure Design), and James Maliszewski (Grognard). Interview with Harold Johnson (Original Co-editor). Scan of the first printing of B4 and a scan of the cover to the “red banner edition.”
Comments: Probably the weakest OAR in terms of historical content/analysis.
Feel free to ask any follow-up questions. Was fun browsing through all of them like this - though it made quite the pile on the couch!