Here's Mud in Your Eye
I honestly don't even want to go into the whys, such is the sour taste the game has left in my mouth, so let's just say the physics are entirely broken, the graphics are deplorable (it honestly could be mistaken for a PS one game at times), the online was wonky and laggy and the game just plain doesn't feel like the same product as the PSP or next-gen versions. It's not even a case of the other games looking better, they play better -- infinitely so -- and the PS2 version just shouldn't be bothered with.
If you have to play another MX vs. ATV game, go get Untamed on the PS3 or PSP -- or better still just play the previous ones on the PS2. Not only are the older games an order of magnitude better than this dreck, but they're probably a lot cheaper at this point too. Seriously, stay far, far away from this game on the PS2. It's not worth it.