It's a monster hunter simulator. No story; you hunt monsters. Menu boxes and horrendously complicated armour sets/requirements make it a stat-lovers wet dream. Combat is solely skill based with the only variables being armour buffs and weapon upgrades. It's tough; damn tough; the only way to play it is with a curled left forefinger on the d-pad to operate the camera.
Once it clicks though it's awesome; easily the best game on PSP and has serviced me for 150 hours and I still haven't got past Hunter Level 1.