Since this is a D&D challenge, I am going to stick to things with the Dungeons & Dragons logo on it. That will include officially licensed and approved products. Fortunately for me, my absolute favorite setting falls under that umbrella.
I love the Judges Guild "Wilderlands of High Fantasy" setting, which is approved for use with Dungeons & Dragons. These products are kind of raw. Granted, over the years there have been some refinements to the setting products by other publishers and writers. Deep down, there is just something fulfilling about this, dare I call it, bare bones setting. The hex-crawl nature is an obvious throwback to Avalon Hill's "Outdoor Survival." It is also the home to my favorite module, which I will post about in a few days.