From Tales of the Grotesque and Dungeonesque; "The most compelling reason to play older editions of the game (or new games that take inspiration from those older editions) is the ridiculously weird and unnervingly unique game materials being produced for those games by the diverse authors and artists involved in the OSR. The OSR embraces self-publishing and the DIY aesthetic; anyone with a crazy idea and the backbone to do the work is encouraged to unleash their strange and uncanny game ideas onto an unsuspecting public.
The best works of coming out of the OSR are delightfully off-kilter. These are the books that would never make it through corporate approval, the auteur works that could never be designed by committee, the real-deal fantasy."
I don't really follow trends in the hobby very much. In fact, I hardly gamed at all in 2015 to be perfectly honest, although we've now restarted our (slightly reconfigured) gaming group back up again with a Call of Cthulhu campaign based on the Horror on the Orient Express megamodule, and I've certainly tinkered plenty with my own m20 rulesets and my settings. I'm not sure if I bought a single RPG product in 2015 (maybe my pdfs of B/X were early in the year? I can't remember for sure.)
So, I'm reasonably out of touch with what D&D 5e is doing, and I'm reasonably out of touch with the OSR (and other gaming) blogosphere, and I've even lost touch with most of the blogs that I used to follow somewhat regularly. It's curious to me, though, since belatedly discovering Jeffro's Appendix N survey and reading through most of it, to have pointed out to me the obvious (in hindsight) generation gap between source materials that older gamers utilized and the newer generations read. And it's curious to me to see hinted that the OSR has, in many ways, become the standard bearer for the older generation's style of fantasy—not style of game, which is what I assumed, but that style of fantasy, which is very different. I've always thought of the OSR has being more focused on the rules rather than the tone and setting, and I think that was definitely true back when Labyrinth Lord, Swords & Wizardry or especially OSRIC were brand new. Perhaps now the rules have become somewhat more unimportant and the way we play, and the types of settings we use, and the DIY ethic with really wild and woolly weird tales is what the OSR means? If so, I need to give it another look... But that's not how I originally saw it. And looking back at the older products, its not necessarily how they were sold either. There's more in common between the G-series and D-series of modules and the extruded fantasy product of Forgotten Realms than most gamers admit; there's very little of the truly extraordinary weird tales vibe in most of the earliest D&D products. The Appendix N is much more varied and diverse than the game itself which references it—although the game occasionally allowed for and hinted at more. Curiously, even back then, those hints didn't often go over well; Blackmoor was never as popular as Greyhawk, and Expedition to the Barrier Peaks was clearly a very polarizing module—a cult classic at best, not one that gamers return to time and time again to revisit (like Keep on the Borderlands was, for instance.) And neither of them are really anywhere near as gonzo as something like, say, Carcosa.
I read recently on Cirsova's blog that 5e was oversold in its appeal to the OSR. It's basically a warmed over, dumbed down, simplified, improved, modified (whatever verb you want to use to there, but you get the point) variation on the 3e experience. My own experience with 5e is non-existent, but that rings true, and I'll believe it. And as Jack Shear noted above, old school is in many ways antithetical to the Extruded Fantasy Product that D&D has evolved into. To the extent that the generation gap separates wild, earlier fantasy from extruded fantasy product, then the differences are probably irreconcilable, and that's that. D&D is now Terry Brooks and David Eddings and Forgotten Realms, and the OSR will be playing ACKS or Lamentations of the Flame Princess and they simply don't have anything in common anymore except the shape of their dice. And then the odd ducks like me kind of go our own way, sympathetic to some aspects of both camps, yet also virulently opposed to other aspects of each camp. For me, I'm more a fan of some of the implied settings of the weird tales than of warmed over Tolkien also-rans, but I'm not a fan of OSR-styled rules systems. Then again, I'm not really a huge fan of highly detailed 3e, Pathfinder or 4e style rules either; the "My Precious Encounter" aspect of those games, or the constant need to reference volumes and volumes of obscure and esoteric rules lore to play it "correctly."