The PS2 has one of the most diverse and stacked gaming libraries in the history of gaming. However because of this many games continue to either be under appreciated or unnoticed entirely. For a brief moment I would like to shine a light on some of these titles. (For the sake of my audience I will only be choosing US titles. Maybe if the response is good I will do the same for imports)
Zone of Enders - Why is this game under appreciated? Probably because its developed at the same studio that works on Metal Gear. Any game short of a pokemon would be unnoticed at that studio. The genre of the game is action, and its sci fi story has lead to not only another sequel on the ps2, but a gba side game.
Makai Kingdom: Chronicles of the Sacred Tome - WHAT? You Mean Nippon Ichi Software produces games other than Disgaea? Coming out in-between Disgaea 1 and Disgaea 2. This game got lost in the shuffle. The typical Nippon Ichi sprite work, and classic SRPG game play might leave one to believe this game is lacking innovation. You'd be wrong. The game is one of the first SRPG to have vehicles on the battlefield (way before Valkyria Chronicles).
Shadow Hearts: Covenant- A sequel to an equally under rated PS2 rpg, this game took everything from the first game: its patented ring system, characters, spooky atmosphere and took it up about 10 notches. When people talk about the best RPG's on the PS2 most people go to suikoden, wild arms, final fantasy, ect. But I think this game is just as good as anything.
Gitaroo Man - Released well before Guitar Hero took the music game genre by storm, Gitaroo Man required the same quick reflexes to hit the notes. What was different however is you werent a rock star, you were a hero whose job it was to battle evil!!!!
Fire Pro Wrestling Returns - Why did this make the list? well its my favorite wrestling game of all time and its not a WWE game nor does it have 3d character models. Not only is the game pure sprites but it doesnt even have real wrestler names ( although you can tell who people are). The game has by far the deepest character creation/move pool of any wrestling game ever made which has lead to a cult following ever since its release in 2007.
Okage: Shadow King - One of the very first rpgs for the PS2, this game had a rim Burton kind of vibe to it. Very strange characters highlight an adventure that didnt last long but it was memorable.
Destroy All Humans! - I remember watching a feature on G4TV about this game right before launch and thought it looked hilarious. After playing it, the game wasnt as funny as I originally thought but I had a blast with it. Nobody talks about it, and every so often I pop it in my ps3.
Onimusha - The series makes use of the historic figures that shaped Japan's History, retelling those stories with supernatural elements. I always found the series one of Capcom's best, but never getting the proper kudo's. The games are action adventure games with minor puzzle solving elements.
Rogue Galaxy - Level 5 burst onto the scene during the PS2 era creating such classics as Dark Cloud and Dragon quest VIII. Those are the games people remember when they think of Level 5. However towards the end of the PS2's life they created one more rpg for the system. It took the creation depth of Dark Cloud, added in the superior cell shading of Dragon Quest VIII with a dash of Star Wars, and that is basically what Rogue Galaxy is.
Sky Odyssey - This game was an action adventure flight simulator released in 2000. I have never been tested so much in a sim like game nor have I ever felt like I actually had skills in a flight sim. The game was critically acclaimed, but sales were not high and was quickly forgotten.
I hope people are happy with this list. I have been reading tons of PS2 lists which all mostly have the same games and I got inspired to do something different.
If I missed a game you thought was particularly underrated please let me know in the comments below.