Ratchet and Clank is a great series, and so are the Jak and Daxter series; both are excellent platformers for different reasons. Although, it might be easier to play Jak 1 and 2 through OpelGOAL, which will run the games natively on the Deck instead of emulation and isn't too hard to set up.

It's a bit of a black sheep, but Spyro A Heroes Tale is a guilty pleasure of mine. It isn't as great as the original Spyro trilogy on PS1, but it's entertaining in its own right. I'm currently playing through it and enjoying it.

I'm running off of pure nostalgia here:

Armoured Core 3

Any of the Ratchet and Clank games

Spyhunter 2 - great local coop

Just throwing Tokyo Extreme Racer Zero into the mix.

I came here to make sure outrun 2006 is mentioned. Try it!

(Also SC2, Burnout and Gradius V but I saw those mentioned)

Highly recommend playing 'Forbidden Siren', but WITH A WALKTHROUGH. Amazing and scary story, but for a slow gamer.

Silent hill 2 Tekken

But my actual favorite was guitar hero.

Ratchet and Clank is the best, and the story is best experienced in order but the first game is a bit clunky so starting on the second game isn’t the worst idea. I personally started with Up Your Arsenal! then got hooked on the series and backfilled.

Mister mosquito

Shadow of the colossus

Robot Alchemic Drive

Dark cloud

Dragon quest 8

Super monkey ball

Twisted metal black

Soul Calibur 2

The original Yakuza games! Yakuza and Yakuza 2. There is a patch out now to for the original Japanese dub for the first game

SSX Tricky, and any of the NBA or NFL Street games, they’re all gas, no brakes. If you can get someone else to play two player (don’t know how well that works on steam deck emulation), check out Cookies & Cream. It’s one of the more clever two player co-op puzzle games, and it’s one of the first games my wife and I played together when we were first dating.

Burnout 3 is one of the best arcade racing games for this generation.

I see you have Kingdom Hearts II in there. There's also the original Kingdom Hearts as well.

The Simpsons: Hit & Run is like GTA but more "family-friendly".

There's also other Ratchet & Clank games on the PS2, including the original, Going Commando, and Deadlocked.

If you like racing games, Need for Speed: Underground 2 is one of the best games in the NFS series. IMO it's better than Underground 1.

Also, appreciate the guide for higher res textures.

Not played by many because it's one of the last releases on PS2, but if you like horror games then check out Rule of Rose. Up there for some of the best graphics on the console too.

https://en.wikipedia.org/wiki/Rule_of_Rose

Others are suggesting Resident Evil Outbreak File 1 and 2. It's much better played online with other people than AI. There's fan server support: https://obsrv.org/ (you have to make an account to see the forum, sorry) and they have guides to set it up on PCSX2. I'd recommend learning how to install it to the virtual hard drive because the loading times are pretty awful otherwise and server hosts generally only make hard drive install only servers.

Their Discord community is a good way to find a group to play with, unless you have a few willing friends :)

Metal gear solid 2: snake eater

R-Type Final -- more than 100 fighters to unlock across a branching campaign, including at least one secret stage.

I was a little disappointed with R-Type Final 2, but I might need to just play more.

I will ALWAYS suggest amplitude (sequel to frequency on PS1). Best rhythm music game ever.

Robot Alchemic Drive

Persona 4 and Clock Tower 3

I love Magic Pengel and Graffiti Kingdom. First is a turn-based JRPG, second is an action platformer. Both share the same gimmick where you collect materials to make the characters you play with the clunky in-game 3D modeler.

I'll recommend Kinetica. It's a one-of-a-kind racing game where you race through gravity-defying tracks as a person in a kind of iron-man negligee with wheels while listening to old-school techno.

Shadow of the Colossus is one of my favorite games ever, battling entities big enough that you run around on top of them, subtle storytelling, an enormous map for the time it was made, and fairly large even by modern standards.

The Tenchu games are also good: ninja stealth assassination.

Dark Cloud 2 is a kind of fun game. Smack your way through dungeons with a wrench and use the bits to build villages for your allies.

Bloody Roar is a favorite for fighting games. Fight to BIOS energy then transform into a wilder form, like a mole, a bear, etc. and you can kick people through the edges of the arenas into new areas to fight.

Devil May Cry is a classic.

Ratchet and Clank, classic.

Time Splitters is reminiscent of even older games.

Red Faction 2 wasn't a bad little shooter.

Twisted Metal Black Shin Megami Tensei: Nocturne (there are pc/steam remasters which are good, but this was my first Atlus game when it came out and it was fantastic to me). any/all of the Sly Cooper games Burnout 3 Robot Alchemic Drive Armored Core (any of the ps2 releases were good I think) Ace Combat Pro Evolution Soccer 5, 6 or 2014 Onimusha Tenchu I didn't play it originally but I've heard good things about Auto Modellista

Steambot Chronicles is my favorite game of all time. It's not well known, but absolutely incredible.

Final Fantasy isn't continuous. Aside from races, the occasional character name, and some thematic elements, the games are not connected at all. PS2 has two of the best: 10 and 12.

Of the two, 10 is a more traditional turn-based experience with notoriously awful-in-a-good-way voice acting and a very typical FF plot. It's not really a spoiler to say that you end up killing god. It features some of the most egregiously awful mini games to grace the franchise. And if you want some of the best gear in the game, you will be committing a not -insignificant amount of time to frustrating button mashing.

Square tried a whole bunch of new stuff with 12 including realtime, MMO-like combat and a much smaller and focused narrative that is mostly a side story occurring inside a larger narrative. The voice acting is infinitely better than 10's, and there are no obnoxious mini games.

They're both still worth playing. The PC ports don't add all that much to the games over what you can do with them emulated. In fact, I bet save states make some of the mini game awfulness of 10 better.

I did not intend to write an essay...