I felt the same way the first few occasions I played it, but then JP grew on me, and admittedly art is not a big concern with me.
I would suggest playing it more and getting deeper into the game.
There is a lot to do, and there are some cool and unusual features in JP (2 way left ramp system, spinning jeep, loopy right ramp).
One of Stern's bests titles in the last 3 years - one of the few well coded games also.