Half-Life.
Champions: Return to Arms (and the game it’s a sequel of, Champions of Norrath: Realms of Everquest).
It’s a quite pretty top-down run-and-slash. But you’ve gotta play it with more than 1 person (and it supports up to 4 with the multitap). Although allied throughout the campaign, inventories are separate and competition for swag can be fierce. You can import your person from the first game into the second game, which is win.
Shadow of the Colossus, no question
I always liked Ratchet & Clank.
Kingdom hearts? Guess not. Shadow of the colossus. Guess yes. 
Everything about this game was done right. It followed the story and style of the movie without fault, even adding in prior backstory without conflicting with the film.
Cutscenes were excellent, as were the characters, their animations and the voices (most of which were done by the original actors).
The controls were fluid, simple and downright easy to use. Fights rarely felt repitive, owing less to the different moves available and more to the sheer variety of levels experienced. Gameplay was good simple fun, striking a perfect balance between combat, small navigation challenges, looting, spraying and even some proper exploration.
The soudtrack was excellent, using a lot of original music, newly composed stuff which still kept the style and even extended tracks from the movie trailers.
Topping it all off was the old Rockstar touch, with the tongue in cheek humour, odd achievements/challenges and highly entertaining “Unleash the Fury” gamemode.
I played the living fuck out of this game, and the only thing that it suffers from nowadays is the incredibly outdated graphics, which is more than made up for by the rest of it. See the movie and play this game today.
A tie between Killzone and Socom.
+1 on Shadow of the Colossus
Metal Gear Solid 3 (Subsistence, so you get camera controls)
FFX was ground breaking but the ultimate FF on ps2 was FFXII. THE game of games on the PS2 however had to be Shadow of the Colossus.
Man I don’t get the love for FF. It’s your regular rpg story except with a lot of detail in each character. The rest is just almost the same as all the other japanese rpgs.
I think you just answered your own question?
MGS2/3 and San Andreas.
Shadow of the Colossus and GTA San Andreas
San Andreas or Timesplitters: Future Perfect.
Timesplitters was the first game I tried to get 100% in with all of the challenges. After 35 hours of gameplay, I had roughly 40% of the game done. It was amazing fun.
Oh man mine was Mercenaries: Playground of Destruction
Best game ever…
San Andreas SUCKED on PS2, it was laggy and slowed down to load when you went too fast, my netbook is more capable of GTA SA than a PS2.
But it originally came out on the PS2 which is why a lot of people are listing it.
Silent Hill 2 :jizz:
hitman blood money. aklso the best game on pc, xbox, xbox 360 and maybe ps3 im not sure