I was wondering when you'd bring this one up...
This has been by far my favorite of all the old modules. Why? Because it and B2 (Keep on the Borderlands) formed the basis for my homebrew campaign world. It's the first place that two separate groups of players, spaced about nine years apart, first got their taste of my Alyxia Campaign. I set the fort the PCs started from as both the starting point for the Hill, and for the Caves of Chaos (I placed the hill nearby and the caves farther out). The Hill bloomed into a trackless magically encroaching forest (Similar to the Fangorn Forest) just beyond a river that separated it from the fort, and the Forest was home to large bands of humanoids pushed out by the human/elf/dwarf/halfling confederation.
The Neanderthal Tribe (I revamped them into a Dakon Tribe), The two little old ladies Rosabella and Rosalinda, and the Forgotten God the monks worshipped I expanded upon GREATLY, and each became fixtures in my game. The adventures of both groups NEVER discovered the Dragon, and BOTH soundly trounced the Hobgoblins on the Hill.
Interesting side note: The PCs in the first group found a helm of opposite alignment (one that constantly worked, but only once per individual), and after subduing a raiding party of Hobgoblins, they used the helm on them all for fun. I decided that the opposite of a Lawful Evil Militaristic Hobgoblin type would be more like a 1960's style peace-and-love chaotic good hippy-type, so they created a Chaotic Good Hobgoblin commune that exists in my homebrew to this day. They even helped save them from "normal" hobgoblins looking to do them harm on a couple of occasions.
In short, I've cannibalized this module in every way, shape, and form for my home games.