Well this is sort of a good game.
Okay I wouldn't say that this is a good game after all, but I find this a bit challenging then any other game I played from gamezhero (referring to some 2014 games that I know of).
In order to beat other levels the key is to have some nitro, you perform tricks at some hills on certain levels.
Here are the times I've goten the stars at (NOTE: Correct me if I'm wrong about the certain time you have to beat depending on the level).
My time: My guess you have to get under:
1st level: 19:36 seconds 20 seconds
2nd level: 22:34 seconds 23 seconds
3rd level: 26:52 seconds 27 seconds
4th level: 25:52 seconds 26 seconds
5th level: 21:19 seconds 22 seconds
6th level: 20:93 seconds 21 seconds
7th level: 22:99 seconds 23 seconds
8th level: 17:92 seconds 18 seconds (?)
9th level: 28:69 seconds 29 seconds (?)
10th level: 36:46 seconds 40 seconds (?)
Well I hope this helps people who are trying to get these medals (no wonder they all have 50 points each).
What I criticize about this game is that sometimes I find the nitro useless (especially when you're mid-air and you do have not much left). Sometimes you can't roll over (while in mid-air) two times instead of one and rarely you might not start the motorbike.
Good game, but it could be improved.