This one I'm going to limit to games that are only on the PS5 since a lot of games are cross generation. So it would be a bit redundant to have PS4 games on this list as well. 

For me, my favorite next gen exclusives have been Ratchet and Clank: Rift Apart (5th poll I've had R&C in my list), Spider-Man 2, Astro Bot, Returnal, and Demons Souls. I know Astro Bot just came out but it's so dear to me that I had to include it in my list. 

No cross-generation? I suppose that leaves out Forbidden West, Elden Ring, God of War:Ragnarök, Octopath Traveler II and quite a few others. My list would then be:

1. Final Fantasy VII Rebirth
2. Final Fantasy XVI
3. A Plague Tale:Requiem
4. Astro's Playroom

Do you think that’s a bad call? It’s awkward this gen because last gen hasn’t completely ended still. 

Astro Bot!

With honorable mentions for Astro’s Playroom, Ratchet & Clank: Rift Apart, and Silent Hill 2

Returnal, as i havem't played astro through astro yet. Returnal nails it in all areas. Great graphics, best use of 3d audio and dual sense control haptics . The gameplay is also sublime.

Again. The Witcher 3.

There's much I have yet to play but with the next gen Patch I can't see it being dethroned. I'm hopeful Baldurs Gate 3 will be good enough to move it out of the top spot but after 20 hours, I'm not so sure it's well adapted to console with the scroll menus even though it's fantastic so far.
Of I were to choose first party, From what I've played Returnal is the best so far. Quite disappointed in Demon souls remake, perhaps that game was over rated to begin with but it's definitely the best looking by far. GTA6 might take the spot if R* evolves their quest design to be less linear and more intertwined like an RPG and they add RPG choice elements among a few other things the series needs changing on but the main characters look uninteresting and the tone is too true to life, I have my doubts. Fingers crossed The Witcher Polaris is released this gen and doesn't become another Cybperpunk situation where you have to own a monster rig or upgrade to 10th gen to play the game thebway it's meant to be played.

ig Astro? idk haven't played anything else.

Read the OP. No crossgen games. PS5 exclusives

For me? I think it's FF16. It was a masterpiece, imo, and only got crap for being different. It's the first FF I couldn't stop playing since FFX.