Ninja Warrior is a game show from Japan (where it's called Sasuke) that is shown regularly in America on G4. Basically, they have 100 contestants that run through four stages of obstacles with the first, second, and fourth being time-based. Anyone who can go through all four stages without being eliminated can claim the title of Sasuke. As of right now, I can only remember two people who have accomplished this feat, and they've shown at least the 13th iteration of the show in America.
Anyway, here's my take on the obstacles,
One I would like to try the most: Warped Wall
Personally, I think I could climb up this beast in one try. It doesn't look too high and people always get stopped by this obstacle.
One that looks the hardest: Globe Grasp
At the point the contestants reach this, they've already been through two or three obstacles that have strained most of their upper-body muscles. I wouldn't mind trying this obstacle though.
Of course, the final stage of the straight-vertical Spider Climb and Rope Climb in 30 seconds is just ridiculous, especially after going through the first three stages.
Edit: I forgot to mention, but the producers also try to add an international flavor to it by inviting notable personalities from different countries to participate. Off the top of my head, I remember Morgan Hamm, US Olympic medalist, (his brother too, I think) as well as other foreign athletes (usually gymnasts) participating.