So, if you like that sort of old school sensibility in play, whether with the old rules or new rules, articulate what about it is fun for you.
As a player, at it's core, it's more challenging and it's more reliant on me as a player. The mechanics are harsher with death far more frequent than modern expectations, so that forces me as the player to think more. I as a player have to think and work out puzzles; I have to think of tactics and strategies, ways around combat, or how to defeat an enemy before rolling the dice; I have to describe things well or I might miss something; I have to think and ask questions or I might miss something; I have to investigate scenes and look for clues; I have to piece together any clues that I find. So most things that my character overcomes in the game is something that I've overcome as the player. Character resources are scarce so I have to manage those resources well or my character dies. That's fun. That's tension and drama. Things like light and darkness actually matter, so we have to manage those resources well or bad things happen to the characters.
To jump to other games for a moment. It's like the difference between Diplomacy and Risk. Both are great games but they have fundamentally different styles of play despite roughly similar goals. Conquer the world. In Risk you move pieces,
roll dice, and take over lands. In Diplomacy you move pieces,
personally negotiate with the other players, and take over lands.
Like with OSR play, that personal touch of me as the player doing things is far more engaging and rewarding than throwing dice.
As a referee, they're mostly all rules light and the play culture and expectations are more in line with how I run games. I'm not interested in thumping rule books and stopping play to look things up. Rulings, not rules. I am more interested in verisimilitude and things being (mostly) more logical, like just characters straight up dying from certain things rather than taking a few hit points damage. Play worlds, not rules. The players expect house rules and accept most without batting an eye. Home brewing, the DIY aesthetic, and getting weird with settings, monsters, characters, magic items is absolutely my jam. While those things do, sort of, exist outside the OSR, they're the beating heart of the OSR.
Details that might also be interesting to know is your history with D&D and whether you played Old School when they were new, as well as what games you started with at whatever age in whatever era. I know we skew a little older here (I am a GenX Metzner Boxed said kid myself) but it isn't universally true with forum users I don't think.
I started in 1984 with B/X. My oldest brother had a group playing AD&D. He is a collector so already had whatever BECMI boxes were out. But Basic D&D was seen as the kid's table game and B/X was the older and therefore "worse" version, so I was allowed to read that. Needless to say I was and still am absolutely hooked.
My current favorite OSR or adjacent games & books are: Acid Death Fantasy, Black Sword Hack, Cairn, DCC RPG, Five Torches Deep, Monster Overhaul, Old-School Essentials, Pirate Borg, Troika, and Ultraviolet Grasslands.