It was new in that it was computer controlled. General Electric had demonstrated a 4-legged walking truck in 1965.[1] Arms and legs were slaved to the operator's arms and legs. It was very hard to drive. Trying to do that with computer control in 1985 was worth trying.

Building the prototype at full scale, not so much. If they'd gone through a few iterations starting with a dog sized version, it might have worked out better. But there was a political problem. DARPA funded a pony-sized legged walker in the late 1960s[2], and it was publicly shamed as a waste of taxpayer money by Sen. Proxmire. So DARPA went for one big enough to carry a real load.

Early thinking about legged locomotion was all about gait and foot placement. It turns out that balance dominates foot placement, and slip control dominates balance once you get off the flat.

Today, most of the problems have been solved, and there's still no market. Which is disappointing.

[1] https://youtu.be/coNO9FpDb6E

[2] http://cyberneticzoo.com/walking-machines/1968-phony-pony-fr...