Ok guys here's a good hidden gem. I bought this game one day not knowing what it was and when I popped it in it said it was made by Treasure. Turns out it's Treasure first 3D style game and "typical" Treasure craziness called Stretch Panic. 

Indigo Prophecy by Quantic Dream:

^ Indigo prophecy is awesome. Basically heavy rain, i think it's even made by the same studio.

All solid and never really talked about.

Off the top of my head, and what doesn't seem to have been mentioned in the OP:

.Hack//Infection
.Hack//Quarantine
.Hack//GU Vol 1-3
Ar Tonelico: Melody of Elemia
Ar Tonelico 2: Melody of Metafalica
Arcana Heart
Armored Core 3
Baldur's Gate I and II
Baroque
Capcom Classics Collection Vol 1 and 2
Castle Shikigami 2
Chaos Wars
Crimson Sea 2
Crimson Tears
Dokapon Kingdom
Dragon Quest VIII
Drakan: The Ancient Gates
Drakengard 1 and 2
Dual Hearts
Eternal Poison
Flipnic
Frequency
Front Mission 4
Gitaroo Man
Gladius
Gradius III and IV
Gradius V
Grandia series
Growlanser: Heritage of War
Guilty Gear XX Accent Core
Gungrave series
Half Life
Heavenly Guardian
I-Ninja
Innocent Life: A Futuristic Harvest Moon
Jak series
Katamari Damacy
Klonoa 2
Metal Slug Anthology
Monster Hunter
Neo Contra
Ninja Assault
Odin Sphere
Okage
Onimusha: Dawn of Dreams
R-Type Final
Raiden III
Red Dead Revolver
Red Star
Resident Evil 4
Rez
Ring of Red
Robot Alchemic Drive
Sakura Wars: So Long My Love
Samurai Legend Musashi
Samurai Shodown Anthology
Samurai Western
Sega Classics Collection
Sega Genesis Collection
Shadow of the Colossus
Shin Megami Tensei: Devil Summoner series
Sly series
SNK Arcade Classics Vol. 1
Snoopy vs. The Red Baron
Sonic Mega Collection Plus
Space Channel 5 Special Edition
Taiko Drum Master
Taito Legends vol 1 and 2
Virtual on Marz
We <3 Katamari
Wild Arms: XF
Wizardry: Tale of the Forsaken Land
World Heroes Anthology
 

Marvel VS Capcom 2
Gradius V
REZ
The Warriors
Shadow of the Colossus
Odin Sphere
Metal Slug Anthology

Yakuza 1 and 2?

That pained me. 

Oooh, a Siren spotting. I forgot all about that one.

Too bad the sequel was complete crap.

Awesome list, so happy to see smugglers run, this game was amazing especially for an early ps2 game. I just posted the second above you which was amazing.

Siren is supposed to be great, gotta check this one out. Man by the time this thread is through i am gonna have like 100 more ps2 games on my want list lol 
 

My brother and I played Smuggler's Run and Cold Winter a ton back in the day. 

I like Siren, but it's not nearly as good as some of the other horror titles. Definitely worth picking up however. 

I hear that, man. I have well over 300 PS2 games that I'd consider "good" and "worth owning," and I'm still finding games worth buying and ones that I don't have on this thread.

Surprisingly, there are lots of good ones worth importing, too. It's scary how awesome that console is.

I've heard great things about Siren too. I definitely want to play it. I also never played any Clock Tower or Fatal Frame games. I've been harassing my friend to lend them to me but he keeps "forgetting" every time we hang out. Lol

Rise from the ashes!!!

All this ps2 talk has me wanting to add more games. I updated the list as much as i could. I will run through the thread again and add whatever is missing. Also some obvious ones missing from the list.

I might even try to break the list down by genre, but that could take some time.

Hoping this will eventually become a decent resource out there for people wanting to dive into this massive library.

Has nobody mentioned destroy all humans? There's a gun that makes people shit their pants

Sweet jesus, i have to add so many of these to the OP lol 

Hopefully this list won't become cumbersome to read, i have to think of ways to keep it easy to read and informative. But with 200-400 must haves and hidden gems, could be difficult. I will figure it out!

Anyone has any ideas, my ears are open.

 

Never played it! But it will be added lol I have heard good things about it.



 

Tons of great games mentioned in this thread already.

Just a few off the top of my head that are missing...

King's Field IV: The Ancient City - If you like the King's Field series from PS1, you need to play this game. I'd say it's a tiny bit more cryptic and grindy than the first games, but it opens up into the King's Field we all know and love. (If you happen to love that series that is).
It's still cheap, but a pain in the ass to find. Snag it if you see it.

State of Emergency 1 & 2 - if you are looking for a deep, serious and emotionally fulfilling game... these games are NOT it.

What these games are instead are chaotic and often hilarious. The story is a barrel of shit, but who cares. You run around causing riots -  and everything you find laying around can be used for violence and destruction.

At one point during one of the side missions an announcer comes over the loud speaker and screams "CONGRATULATIONS! YOU'VE KILLED EVERYBODY!!!!"

Hardly wholesome offerings, if you want to partake in some cathartic mayhem, pick up either one of these pieces of crap.


 

state of emergency sounds like my kind of game 

It's really bizarre, sometimes frustrating, but well worth digging through the bargain bin for.



 

Siren is awesome; you'll need gamefaqs just to survive though about halfway through the game. Finding some of the criteria for unlocking next levels is just about impossible. You'll just keep looping while cheap shibito snipers headshot you at the exit goal, ha ha ha.

 

Don't have a ton of PS2 games but I'll second or third or fourth Shadow of the Colossus. Started playing through it again just recently and there is really no other experience like it.

For me Rule of Rose was fantastic! I couldn't put it down

I found this on the PS2 reddit(the most active PS2 exclusive forum I have found) that I think is pretty relevant to this thread:

Photobucket resized the image which made it pretty useless so hopefully this link works
http://i.imgur.com/ISh6EeI.jpg...

^ seeet jesus thats beautiful. Thanks so much. Will put in the first post with the list. This is great and what i planned on doing. Well close. But better.