Kamikaze Midget said:Low complexity?
High Fun?
Pick up the True 20 book. One of the mini-campaigns is "Mecha vs. Kaiju."
It's True 20, so it's very low complexity, and it's high fun, because it's giant things beating the crud out of each other.
jdrakeh said:I'd go with BESM d20 + d20 Mecha.