MX Unleashed for Playstation 2 is the best off-road motorcycle racing game yet. The physics model seems convincing, if somewhat exaggerated to let you pull off huge jumps with ease. It may be the first game to realistically capture the strategy of block-passing -- cornering in a path that is (usually) worse in overall speed, but that blocks the rider on the "better" line and forces him to slow down. I noticed that the crowd sometimes boos when you block-pass, which I found amusing.
Like most motorcycle games, MX Unleashed misses a few real world details. It has only one brake button, not the separate front and rear brakes found on real motorcycles. Oddly, one of the only games that gets this right is Grand Theft Auto: Vice City. And though you can wheelie, the only way to do it seems to be by revving up while holding the clutch in and then popping the clutch. This method is realistic, but in real life you can also wheelie by using the rebound of the front fork. You can suddenly decelerate to compress the front suspension, then snap on full throttle right as the suspension is pushing back up. The game does not allow this, which is a very minor flaw and certainly does not impact gameplay. The fact that I expected this to work only shows how convincing the game is most of the time.
On certain Nationals tracks you can "cheat" by riding on the very edge of the track where there are no jumps instead of going over the jumps. Usually this is much faster. It is difficult to do, though, because if you stray too far off the track for too long you get penalized and lose a huge amount of time.
I wish the game had an "advanced simulation" mode where it is much easier to crash. As it is, the only way to crash is to hit something or land a jump very badly. You never seem to crash by losing traction in a corner, or losing balance on a bumpy section. I guess this gives me something to look forward to in MX Unleashed 2. I highly recommend MX Unleashed for dirtbike fans.