The hardest game that I've played that I have actually owned would have to be Lair. The reason is more because of steering, since you have to tilt the PS3 remote to steer, and when there's so much stuff going on around you, it's hard to concentrate. Plus some manoeuvres have to be done by flicking or shifting the remote, and mine never seems to want to comply D:
At least you get to land in the midst of enemy armies and bite, claw, and burn your way through them
mrcherry - i agree completely with racing games, I always end up hitting the side wall and spinning out DX
Though I did somewhat decently in a recent racing game I had for PSP, and Mario Kart seems playable (so long as its not the Wii one if you have no wheel accessory x.x )