I bought both games and after hours and hours of play it's very obvious that MTX: Mototrax is head and shoulders above MX: Unleashed.
the single player has a lot more options and the controls are a lot better. The game is not as arcadey as MX: Unleashed and really makes you time and work for everything.
I must admit it's a very very hard game, but in the end the rewards are well worth it.
The game sports an incredible track editor where you can build your own tracks...
It also supports 8 player XBOX LIVE play as well as System Link play.
I came off my PGR2 high to pick up a Moto game and MTX: Mototrax has swept me off my feet!