Just taking some time to recommend Cyber Org on the PSX.
This is one of the most obscure games I've ever seen, with hardly any info about it online, and literally zero info or guides on game mechanics, at least in English, which is a shame because this game is pretty fucking good.
The game is in Japanese, but the interface and all the voice acting are in English, so you only miss out on things like e-mails and hints and the game is easily playable even if you don't know any Japanese.
The game is a sci-fi dungeon crawler with action combat. You have a melee combo on square and a special weapon with triangle which is different for each character. The melee is free but the special weapon consumes the blue energy meter. The combat itself is simple and starts out easy, just run up to an enemy, hold R2 to lock on and stunlock them to death with your square combo, but as the game goes on the enemies start getting more aggressive and numerous and they do a lot of damage, and the combat becomes more about positioning and spatial awareness since your combo has a long recovery and an enemy attacking you from behind during your recovery can take half your health in one hit in later areas.
But weirdly enough, the combat is not the central mechanic, that would be the resource management. This is an anti-hoarding game, forcing you to constantly make decisions on what items to pick up and what items to consume. You have three characters with limited inventory, 20 slots each, and you also have a box at save points that can hold 60 items. You can play one character at a time and switch characters when you're outside of a dungeon. Each character has a stamina bar (the yellow bar in the screenshots, called "GP" ingame) that constantly depletes, even when standing still, and when it reaches zero it starts to slowly damage your health and eventually kills you, so you're constantly under pressure while in dungeons. When you're playing a character, the other two will slowly regain stamina, but usually at a slower rate than you consume it, so you'll be under a stamina deficit unless you regularly consume medicines to restore it. Every medicine restores a little bit of stamina regardless of its effect, with the medicine refresh being a full refill, but all the drops are random and the refresh medicine is among the rarer ones.
You usually have to complete multiple floors, sometimes a lot of them, before you find the exit to the dungeon and can switch characters or use the item box, so managing your resources is important, with stamina and inventory space being the two that force you to make decisions most often.
Killing enemies and destroying things gives you something called Access Points (AP) which you spend when interacting with terminals. You need to use terminals to unlock doors, unlock the teleporter to the next floor, get the floor map, and a bunch of other things. You generally get way more AP than you need, so I'm guessing it's just there to prevent you from running past enemies, since you won't be able to use terminals unless you kill at least some enemies.
Sometimes you will run into a dungeon that only a specific character can complete, and you'll be under extra pressure if that character happens to be the one who just did the previous dungeon and is tired. So far I've found three types of "barriers" for specific characters. When entering a room triggers an alarm and starts spawning infinite enemies, you're supposed to use T.J. (the blue guy) and use his stealth camo to sneak past that room (hold circle for a few seconds to activate it). Whenever there is a platform you can't jump high enough to reach, that's meant for Fosis (the purple bug guy) but you can also use a medicine jump. Finally if there is a strange wall that has a hit effect when you attack it, but doesn't break, you're supposed to use Gigante (the big green guy) to break it. These hard barriers are always on the first floor of a dungeon and that floor will always have an exit portal so you can get out and switch characters. I'm leaving that info here because I got stuck at those parts for a while.
As weird as it sounds, I would recommend this game to people who enjoyed all the decision making with the inventory management in games like Resident Evil. The way you have to decide what to pick up, what to leave, what to consume and what to throw away feels kinda similar, you're constantly juggling resources to progress. It's not just what you need to consume to refill your bars, you also have to power up with drugs to keep up with the enemy power creep. It's a repetitive game, but it's one of those repetitive games where the constant pressure to move forward while juggling all your resources gets so addictive you don't really mind the repetition.
Oh, and the game supports the dualshock and I would highly recommend using it over the dpad. This game has better camera control on the right stick than any PSX game I've played, it's even better than some PS2 games.