Trials HD is a 2.5D game, 3D but on a 2D plane. It is a motorbike game where you have to move over obstacles, drive up ramps and use your balance to reach the finish line. It is very similar to Across (action cross) and the later Elastomania and all those clones that have popped up over the years. But there is a few differences namely.
1. You dont jerk your bike violantly forward-backward, it is much smooter leaning with the left analogue stick which makes the game feel very different.
2. You cannot turn your bike around to go backwards, you always move left to right towards the finish line.
3. You do not collect apples :)
The graphics looks very nice and more importantly the framerate is very solid and smooth. The game is divided into differnet difficulties (easy, medium, hard, master and so on), with bronze to gold medals to be won for completing each track in a certain number of checkpoint retries and under a certain time.
Also there are minigames which differ somewhat, like catapulting your racer from his seat down a set of stairs to break as many bones as possible, flying through rings of fire, hill climbing and so on.
The controls are spot on, very responsive and accurate. There is alot of trial and error in this game, but the reset button reloads instantly which makes you wanna try just one more time. I reached 180 retries on one track so far .... but there is great satisfaction when clearing a track.
Sounds are well done as well, you can hear your speed and momentum, the soundtrack is great.
There is also included a level editor in this game which seems very detailed if you go enable the advanced editor mode but the biggest drawback with sharing levels is that you can only do it with people in you friendslist. Hopefully they will patch the game to have community downloads or something.
Overall this game would have gotten 0.5 stars more if they just included a reasonable way to download user created tracks. Nevertheless it is an awesome game.