i don't want to get stuck arguing over definitions - whether a game "counts" as OSR is less important to me than what all the game's dynamics accomplish when put together. my post here is less "OSR means this and only this" and more "this is
what i like about the OSR games i've played".
- combat as war, and to a lesser extent, combat as a fail state. combat is unbalanced, unreliable, and very possible to swing heavily in your favor through your approach and preparation before combat actually happens. this isn't to make the game harder, per se - this means i'm always much more lenient about avoiding combat than i'd be in, say, 5e - it's to ensure combat is not a go-to catch-all solution for every problem, it's the risky Plan B you fall back on in an emergency. this puts emphasis on the second point...
- your character sheet is a toolkit, not a restrictive list of all your options. your most effective tool is your wits and your ability to do anything a normal person could accomplish with clever thinking; your class abilities are just a little extra on top of that. (this is also the reason most OSR games are low-power, to emphasize normal-person shenanigans.)
- procedure-heavy. time is tracked for random encounters and dwindling resources. the reliance on procedures eases the amount of GM fiat that goes into running OSR games; if the GM is constantly hand-picking the challenges you'll face, it can feel like the game is less concrete and dampen the feeling that your actions matter. (obviously the GM still decides a lot of things, but this reduces that.)
- designed for sandbox play. the above points feed into this: if the game is about creative problem solving, and there is no obligation to balance encounters, the GM can simply create locations to explore, drop the party into them, and start playing. the structure provided by rules like dungeon turns takes a lot of work off of the GM, and the rules are usually very resilient to player shenanigans that would cause other games to fall apart.
EDIT: oh, i forgot, probably the most important aspect:
decision making. the core of the experience, to me, is taking stuff that's a foregone conclusion or busywork in other games and making it
matter. tracking how many arrows you have is mind-numbingly boring,
unless it matters. you go from annoyed you have to track every arrow to
scared you will run out, so every time you use an arrow, now that's an agonizing decision about whether it's worth burning one of your valuable few chances to attack without the risks of engaging in melee.
tracking encumbrance is boring busywork,
unless what you spend that encumbrance on matters. i have 10 item slots and 5 arrows can fit in a slot; is it worth bringing an extra 5 arrows when that slot could hold a rope, a crowbar, maybe some blast powder, maybe more food in case of an emergency?
inflated economies like D&D has (most OSR games are pretty bad about this, tbh, but it's feasible to fix with houserules) take away meaningful decisions because you'll usually have more gold than you need. throw that out, stop giving out enormous piles of wealth (adjust XP-for-GP math if needed) and always have more stuff the players want to buy than they can get all of. suddenly busywork becomes decision-making. boring gameplay becomes tense, engaging gameplay. and on the plus side players are way more excited about finding gold because it
matters now, as more than just XP in the form of an item.
creating as many meaningful decisions as possible is
the most important thing for me, and overall OSR games nail that better than any other RPG i've played. i don't know how high up that is on most people's "Here's What Makes A Game OSR" lists, but it's absolutely the top priority where i'm concerned.