Easiest way to get a lot of the boost/wheelie/flips based achievements--from the starting line, use someone like Sir Colin or farty pants and simply sit at the starting line and do the wheelies or bunny hop flips to accomplish the task. The other riders will generally be waiting for you about 3 or 4 flags up.
Good start. timing on the platforms is too sensitive (IMO). Lava should be escapable somehow. Better explanation on how the portals work would be good. 3/5 for promise.
very impressed. 4/5. Might be worth throwing together a super easy mode with laser guidance, or a bit of a tutorial (so you don't have to learn that there are no walls on the side the hard way!)
Funny, looks great, I'm shocked the rating isn't somewhere around 4 right now. My only quibble is with the spot-the-difference game, there are more than 5 differences on one of them (due to shadows) 5/5