I like the introduction of new challenges but it'd be nice to see some twists on old challenges, or the return of the REALLY old challenges such as the walking machine :D Can't wait for the Paintball Tanks. Collapsible Cars... well, it's already been done, though it'll be nice to see it done on a show that could care less just how glamorous the cars look. (Panic Mechanics = Too concerned with flashy vehicle appearances) Railroad Racer should be interesting (I'm reminded of the DeLorean from BTTF3) and... well, I'm not sure about the Ice Warriors challenge. A puck shooting machine? Should be interesting :D It's always the 'little object' challenges that seem fun since you're no longer just grabbing old cars and steel beams off the scrapheap but having to rummage for the smaller stuff, the components of other things.
Darnit, I want to see the return of the N.E.R.D.S. though.... I mean, c'mon, the steam car challenge, nobody harped on the "Evils of chain drive" as they have in the latest seasons because the team was doing so great that there was no possible way the chain drive would fail. :D