Great Game. One of the best motorcycle related games I have ever played.
I played the game a lot during the last couple of months and I can say that the game is VERY realistic. The lines you choose and the tactics (trail braking, late braking, gear selection) you apply are crucial if you want to be competitive in the game. One suggestion, try (win) as much bikes as you can to distinguish the characteristics of each one. Also play around with suspension and gearing settings to find the best possible setting for each track. When you do that, and get familiar with the track, there's no way you will fail. Playing with your friends is more fun due to the fact that they are smarter than the bike and can use different tactics to shut the door on you on technical turns, etc.
Also as in real motorcycle track riding, plan ahead on series of curves to leave the turn fast. Entering a curve fast does not guarantee you will exit it fast! Try to locate braking markers and play around them a little to find the best possible combination. Have Fun!!!