Published in 1981, The Secret of Bone Hill is the first module in the L-series, so designated either because it was set on the World of Greyhawk's Lendore Isle or because it was written by Lenard Lakofka, a long-time contributor to Dungeons & Dragons and a regular columnist to Dragon magazine. Whatever the case, L1 is, in my opinion, an under-appreciated classic, a low-level introductory module that nicely occupies a middle ground between The Village of Hommlet and Keep on the Borderlands. Allow me to clarify.
The Village of Hommlet is often praised -- and criticized -- for its mundanity. Hommlet is Exhibit A of Gygaxian Naturalism in action. Nearly every inhabitant of the village is given a name, a personality, and a place within its little society. Likewise, the nearby moat house dungeon is subdued, with a semi-realistic ecology and suffused with a sense of foreboding rather than blatant evil. Keep on the Borderlands, on the other hand, offers very little in the way of context. The titular keep is a lone outpost of undefined civilization, beyond which there exists only the wilderness and the forces of Chaos who dwell within. It's almost purely fantastical in conception and the Caves of Chaos are frequently cited as an example of bad dungeon ecology, with numerous antagonistic humanoid tribes existing cheek by jowl with one another.
The Secret of Bone Hill presents the town of Restenford, which is as well imagined as Hommlet, complete with unique names and personalities for even the most minor of NPCs. In addition, there are maps aplenty for the town and its buildings, making it very friendly to referees who give their players the freedom to wander about the place as they wish. Surrounding Restenford is a dangerous wilderness filled with bandits, humanoids, and other threats. And of course there's Bone Hill itself, home to numerous undead, including such foul things as ghoulstirges, stirges who paralyze as well as drink blood. Bone Hill is a dangerous place, one that beginning adventurers ought to avoid until they've gained sufficient experience to tackle its horrors.
To my mind, the beauty of module L1 is the way it combines the mundanity of Hommlet with the otherworldly fantasy of the Caves of Chaos. Much as I love B2, it sometimes feels a little too de-contextualized -- perhaps by design -- but I find I like context for my adventures, particularly low-level ones. Hommlet and Restenford are both very good "home bases," whereas I don't find the Keep particularly compelling, a problem made all the more obvious to me in my own Dwimmermount campaign, where Muntburg is a close relative of the Keep in terms of depth and detail (which probably explains why both the players and myself prefer to visit Adamas, even though it's farther away from the dungeon).
Bone Hill is a weird place. During the day, bugbears hold it, while, at night, they cede control to the undead who rise up from their graves. This fact gives it a peculiar vibe for me and one that I think helps the module considerably. And the number and strength of the surrounding creatures, both at Bone Hill and elsewhere, ensures that PCs have good reason to spend a lot of time in Restenford, getting to know its inhabitants and their peculiarities, rather than just treating the town as "flyover country" they can simply ignore. The result is a terrific dynamic that I've always liked and that has probably informed my own campaign design as much as anything else.
If you haven't read The Secret of Bone Hill in a while, I recommend you do so. I think you'll find it better than you remember its being and a genuine classic of the early 80s.