If you only ever listened to annoying AD&D fanboys, you might think that the OSR is strictly about crawling through big megadungeons as sword and sorcery murderhobos. But no community should be defined by its worst gatekeepers. The very fact that they suggest the OSR to be anything other than a manufactured revisionist narrative is reason enough for them to be suspect. To me, the OSR is an enduring illusion in large part because it's a very flexible culture of play. And I feel that despite its reputation for being notoriously difficult to define, "old school play" is still pretty cohesive and compelling.
I usually find myself on the side arguing for an expansive definition. "Renaissance," not "revival." The most important non-D&D game in the OSR lineage is Traveller and its relatives, and indeed, moderately-hard sci fi is a cornerstone genre in this space. So too are noir / investigation games and horror games. The genres often get blended together (Lamentations of the Flame Princess, Mothership, Electric Bastionland, Esoteric Enterprises, and Liminal Horror come to mind) but they just as often remain separate! Perhaps these four genres are simply the cornerstones of all RPGs. The most robust and reliable ones you can emulate in nearly any play culture. Remember, Call of Cthulhu and World of Darkness have historically been the biggest serious competitors to D&D globally.
Despite this, I've recently been thinking about some things that have got me feeling out the borders of what can count as "OSR." This is a rare occasion when I'll be the one standing guard at the gate. But more interesting than that, I aim to discuss why these outsider genres can still be very exciting anyway for someone with OSR-inclinations like myself, even if they're "incompatible" with my default preferences.