I’ve seen a lot of videos of various robot concepts over the years–on Discovery channel and such–but none I’ve ever seen come anywhere close to this thing.
Go read about it right here. And, if nothing else, you absolutely must check out the video of this guy in action. The key, of course, is four legs, which means that you have at least two feet on the ground at all times–versus the "infinitely" more difficult problem of a two-legger, where you have significant time with only a single foot on the ground. Perfecting this will probably pave the road to a two-legger much faster. That would be my bet.
They also need to come up with a power supply that’s quieter than a reciprocating engine.
(via my bro, in email)