There's some bangers on ps+. I'm a pc gamer but I've peeked (extensively) at the catalogue and while I still feel Xbox game pass is better value for money, here are some:
Abzu: beautiful game about exploring an abandoned underwater environment
Bloodborne: not "hidden" but a must play
Concrete Genie: Cute little game about grafitti creatures
Dandara: a unique platformer with a great style
Dead Cells: fantastic roguelike
Ghostrunner: amazing cyberpunk parkour game. If you like movement, you'll love it.
Everspace: great arcade space game.
INSIDE: wonderful little game that will have you thinking about what it's story really meant
Magicka: incredibly silly magic game
My Friend Pedro: gunslinging slow motion stunt combat action
Moonlighter: roguelike shopkeeping game, think Reccetear
Party Hard: stealth party killing spree action
Spiritfarer: beatiful game about helping the dead find peace before moving on
Vermintide 2: one of the best horde games out there.
Other ones that are less hidden gems but I conside must plays or at least worth checking out: Bloodborne, Death Stranding, Dishonored, Doom, the Middle Earth games, Shadow of the Collosus
Monster Hunter. I first tried it on the wii u when I was honestly too young to really comprehend what was going on and bounced off. Years later I picked up MHGU and MH World and got basically addicted. Now I own almost all the games physically, as well as picking up a 3ds and Vita so I could play the psp and 3ds games on the go.