Although I contend that The Village of Hommlet, about which I've already written a retrospective, is the greatest exemplar of Gary Gygax's remarkable skills as a designer of adventure modules, I recognize that this is a minority opinion. There's a peculiarly large contingent of gamers who dislike module T1, a sentiment I find baffling. Far more gamers, if asked to choose their favorite Gygax-penned module, would choose The Keep on the Borderlands. To some extent, I suppose such a choice is inevitable, given that module B2 was packaged with the Moldvay Basic Set, through which perhaps more gamers entered the hobby than any other. For these gamers, The Keep is where they first took up their swords and donned their shields in defense of the Realm against the depredations of Chaos. It's a touchstone for an entire gaming generation in a way that the better-crafted Hommlet is not.
This isn't to denigrate The Keep on the Borderlands, whose purpose is much different than that of T1. It's quite explicitly intended, like its predecessor In Search of the Unknown, to be an aid to the novice referee. That's why so many of its 32 pages are devoted to advice and suggestions on running the module and on the art of refereeing D&D. I'm frankly torn in my estimation of B2's success in this regard. On the one hand, it's a lot more structured than B1, with both the eponymous Keep and the Caves of Chaos thoroughly "filled in." On the other hand, this structure might be better suited as a tutorial than is B1's open-ended approach. It's hard for me to judge this, since I came to The Keep on the Borderlands after playing the heck out of In Search of the Unknown for many months. My feeling then was that B1 was too "kiddie-fied," which led me to mistakenly turn my nose up at all subsequent B-series modules until I could be convinced that they were "proper" D&D modules.
Still, there's a great deal to like here and I certainly had my fair share of good times refereeing this module. Morgan Just made his first appearance as a PC in B1, after the death of his ill-named predecessor Hercules (at the hands of fire beetles, no less). Likewise, the Mad Hermit of the surrounding wilderness became a minor patron/villain for later adventures, something the module itself suggests as a possibility. Likewise, the Keep served as a home base for many levels and Muntburg from my Dwimmermount campaign is at least partially inspired by it.
There's no denying that there's something extraordinarily primal about The Keep on the Borderlands. Gygax was always very good at setting a scene and the scene he sets in this module is a potent one: a lonely bastion of Law, defending the Realm against the creeping hordes of Chaos. In many ways, that's the most archetypal description of Dungeons & Dragons ever written. It sums up the game very succinctly and yet in such a way as to leave lots for the individual referee and player to imagine for himself. Whereas B1 is about a dungeon without much context, B2 presents us with a world, one to which even the Caves of Chaos exists in relation. It's a sketchy world, to be sure, but it's a world nonetheless. Perhaps it's this implied expansiveness that makes The Keep on the Borderlands so powerful even after so many years. Its lacunae open up entire fantastical vistas into which our imaginations can expand.
How very Gygaxian.