How realistic giant robots? Like anime robots that are firing giant assault rifles and punching crap realistic? Or walkers of varying sizes and legs, armed with various RCS thrusters (and otherwise) with artificial gravitational plates on the feet to keep it from falling off a low-gravity planet, and so it can maneuver while firing specially-designed recoilless railguns, coilguns, plasma weapons, lasers, and missile launchers in open space kind of realistic?

Usually, anything termed "Mecha" refers to the super-dumbed-down version of phsyics and realism, while "Mech" refers more to the scientifically-accurate, physically-possible side of things. I didn't see the greatness of a robot somehow punching something apart in space- when you can take a railgun, mount it on a reloading mechanism equipped with a couple boxes of ammunition, a small reactor, multiple solar panels, some RCS thrusters, and essentially do the same thing- blast something apart- except from about 50 kilometers away.