Great idea for what it is, but longer races can get tedious and the PS3 framerate is pretty distracting during gameplay.
As for the gameplay itself. I always liked the ATV Off-road series and I like the big open world environment of this game as well. The AI is pretty challenging and even with a jerky frame rate the game is growing on me. Although after 20 minutes of racing through scenery that, at times, has you asking yourself 'haven't I been here before' gets a little tiresome. 20 minutes is the longest race I've tried so far. I couldn't imagine going for 3 hours. But I understand what 2XL was going for with this game. They were trying to give the gamer the hybrid feel of a sim/arcade racer in a big open world where races don't last for just a few minutes at a time.
I would definately recommend Baja as a rental for most people before you buy and if you're a big fan of the original ATV Off-road series, probably a definate buy. It's too bad the PS3 version couldn't run more smoothly though. I've posted a message to the Playstation.com forums (look for 'Baja game' and 'mtnjak'). I'll post updates if I end up getting a new hard drive and seeing if it helps with the frame rate issue any.
UPDATE: It's been about a year and 3 months since this review and about 1 year has gone by since I played it last and I just picked it up and started playing it again. In an effort to save money (I haven't bought a game since the new COD back in November) I thought I would play a "new" game by replaying some old games. Think of it like a child who rediscovers an old toy and it's like it's new again, sort of. The jerky PS3 frame is still there but this is still a fun game to play. I hope 2XL gives it another shot. These guys pretty much own the original physics of the first Motocross and ATV games that I think are still the best game play physics of any of the ATV games out there. I'm still only about halfway through this game. Plenty left to help cope with the cold winter blues.