Nice build and I like the idea, however the artwork is a little bit to much for my personal taste.
Personally I had removed the third joystick and go for the servo sticks in order to have a 4-way option (at least I assume that it is a dedicated 4-way, else it doesn't make any sense at all). Then you would have better access to the trackball as well for correcting the aesthetic part.
The side buttons, are they for pinball games? Then I would have them in the end closest to the player. If not, what are they?
Put a video projector between the speakers and it is truly mobile