Robotics are a problem because there are too many people for too few jobs. Why bother automating when there are masses in China willing to put one screw in one part of one toy over and over again for 18 hours a day? The worldwide unemployment rate is getting worse every day because people will not stop increasing the labor supply. Frankly, in terms of our species and our planet, giant killer robots would probably be a good thing.
As for their abilities? Endless given enough engineers on the task. Right now, the automation variety is fairly fool-proof and the unsung hero of industry in the West. Intelligent varieties will be around eventually, but until they have purpose and meaning in the world, they'll continue to be toys to showcase the research budgets of Japanese companies and Universities in the United States. They might be good for espionage if they can be made small enough.
Large robots? The main problem is complexity and power supply. Something similar could be made now, but again, why bother when you can build 1,180,000 tanks you know will work for the same price? As for the power supply, if you want to build it now, why can't a giant robot run on a diesel-electric system? All you'd be powering are a bunch of hydraulic pumps and servo motors, so it's perfect. Well, it's no worse than carrying batteries anyway.