The OSR game for my Pathfinder crew went well. Since it was a one-shot, I just created characters for them (a process which took < 1 hour for all three) and had them visit (yet another) ancient temple in search of the legendary statue of...y'know, it was just a one-shot.
I had intended to use the night as a showcase for combat tactics, giving them a ruined overground area with rubble, walls, and a couple of hollowed-out buildings so they could play with setting their own traps, exploiting cover, utilizing verticals, and the like. There wasn't so much of that, but there was some old-school dungeon crawling in the secret underground chambers. Since there was no "spot" check, but there were obvious traps, the players were going slow, asking relevant questions ("what do the tiles look like?" and "how many holes are there in the wall?") and making smart decisions ("I can cast Protection from Normal Missiles and set the dart trap off"). Chief among these was the use of the Cloak of the Mountebank to steal the idol and disappear before the ethereal Chimera could materialize and attack, although D., the rogue's player, decided to taunt it before disappearing and lost a dozen hit points from claw/claw/bite for it.
Feedback was positive, especially from the two who'd played 1st and 2nd edition D&D before, but even the one who'd only played 3.0 and later enjoyed it; the general opinion was that they'd felt more immersed because they were really looking at things. A question came up on reddit about how to increase immersion, and (though I didn't post to it), the answer was clear to me: don't have Spot/Sense/Notice checks, but let the players ask about the world around them.
So, it was a good night for showcasing what the old-school does well, and my players like it, but I still want to run a good mass combat one of these days. Fortunately, they've given me the go-ahead to try some more, so I will get the chance to one of these days soon.