i think it would be great to have halo for the psp. unlike other portables the psp has a controller theme to it so most of the buttons u need for an FPS are there. ur really only missing an extra joystick and the two buttons on the end of the xbox controller. the second joystick could be replaced with the arrow keys and then all u need to do is remove the two secondary buttons at the back.

I think it could work :)