GaoGaiGar is kinda childish. But gets increasingly silly and dark as it goes along. Per the directors style. But it has really big stompy robits.
Also the design of the Mechs might be familiar to you, if you have any knowledge of Hasbro toys.
Gunbuster. It's basically a classic at this point. Is set mostly in space, with lots of hard scifi. The robot in it is huge. But the pace is slow.
The Big O. Is kinda like a weird mix of Batman and Phoenix Wright but with a big stompy robot defending a city from other big robots. So it's partially a mystery show, and partially a crime fighting show with big robots.