if you're sticking with the massive weapons then I agree with all the previous comments, the legs need to be designed to provide greater stability, therefore larger feet and possibly heavier legs.
here is a link to the changes I made to the design from the original LDD file, I've given you a credit. I hope that is ok? http://www.mocpages.com/moc.php/294666
I agree with everything you guys said, except for the whole weaponry thing. People carry guns and weapons that are bigger than their arms all the time in real life. Why can't a mech have weapons like that too?
You've got quite a few good mecha concepts here, but some of them are mismatched, as Andrew said. Those weapons are suited more to a larger build. The legs could afford to be reworked, but the torso is nicely done. I do recommend adding a head, possibly more canted foreward than just on the shoulders. And try a compound leg, I think it would suit the design better. Still, very nicely made, and very ambitious. ^Blub^
Hmm, well I have to say, I really like that torso, but I feel that the rest of the mech could use some improvement. The overall joint system doesn't look as sturdy as it should, particularly the joints, and as I've told you before, your weapons are really simplistic and unrealistic. That cannon is interesting, but it's just too big. The mech would fall over, even if you made it out of real bricks, let alone if you built it full scale. Try working a bit more on the realism of your mechs, as well as making them more sturdy, and you'll have a winner for sure.