... except Mekton.
Anything goes as long as there's mecha and they're customizable. And it's not Gurps.
I was thinking about proposing something new to my friends and I was wondering if there was some good games with (giant) robots. Possibly gundam-style mechas (big, not too much, customized, can be broken/repaired/finish ammo).
A good default setting is, of course, a big plus.