It depends on what you call "realistic". When I had seen 50 foot humanoid robots on film they were everything but realistic, also the fact that you don't know

It depends on what you call "realistic". When I had seen 50 foot humanoid robots on film they were everything but realistic, also the fact that you don't know how a 50 foot robot really behaves helps a lot. Normally they hide the problems using light, making it dark, like a night scene. Making video realistic with bright light is really really hard and really really expensive because in the real world there is dust and rust, and dirty mud and imperfections everywhere, but those are hard to model. Even then most film professionals will know instantly is something is created digitally. It is exponentially more expensive to improve in this area, so they compromise on what most people would consider ok for the least price. Even super expensive productions like Starwars look very artificial for the trained eye.