I bought Trials HD for the xbox360 on xbox live and spent 1200 MS Points for it. And I can only say – it´s great fun. Due to the HD resolution the game looks brilliant. The levels are well designed, start easy and then have a good learning curve towards some really fucking hard levels. The controls concerning the bike are limited to accerleration and braking. The more important part is the steering of the driver which is done through the left analog stick.
You can get a first impression from the following video :
Some of you might remember this kind of games from several browser games available online. But the origin of this genre might be ExciteBike published 1984 on the NES.
If you wanna know more, then check the Wikipedia artcile, otherwise if you wanna travel back to 1984 then here´s your chance to play it online :