Quirky/Unpopular/Good PS2 games

What are some good quirky, weird, unpopular, "hardcore" ps2 games?

God Hand would fit all three of those descriptions, although its loyal cult following does appear to have gone somewhat mainstream now.

The PS2 version of Shinobi is an excellent, underrated and very very hard game if you're in the mood for that. There is also the sequel Kunoichi.

The success of these games is debateable, but they are all great quirky hardcore games:

-Beyond Good & Evil (action RPG-ish)
-Psychonauts (platformer)
-Indigo Prophecy (no way to really describe)
-Shadow of the Colossus (boss battling open world RPG?)
-Okami (RPG)
-Black (FPS) - Great bullet crazy game!

And the last is just a guilty pleasure because I'm pretty sure it's not that good, but it's cheap:

-Oni

Hope this helps!

• Dororo (Blood Will Tell)
  
• I.Q. Remix+: Intelligent Qube
• Stretch Panic
• Contra: Shattered Soldier
• Maximo: Ghosts to Glory

If you like RPG's Shin Megami Tensei: Nocturne. If you can still find it. One of the best RPGs ever made although not many people have had the chance to experience it. I wrote a review if you're interested.

http://www.gamespot.com/ps2/rpg/shinmegamitenseinocture/player_review.html?id=214326&tag=contributions;review8