Onimusha kind of sucks. The controls are wierd, the story is wierd, and it's hard.
As for the PS2, I always suggest Suikoden III, awesome game, great story. That may not be what you're looking for but it just has to be said =).
Old NES/SNES Zelda like games for the PS2, that's kind of hard. Baldurs Gate: Dark Alliance comes to mind when I think of Zelda and the PS2. Course BG
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A is sans all the neat puzzle dungeons, it's the best I can come up with for comparison though.