An awesome sight it instantly draws in the viewer with its action and scale, the classic battle between military and giant crazy robot, probably my favourite subject matter for an epic painting, but there are a lot of them so its hard to make a painting in that subject more original but your vision of the robot is pretty unique, don't think I have ever seen a giant shark robot with legs before.
Now for some critique, your painting technique is great as is the lighting my only real gripe about the image is the scale, the robot both seems to be huge and yet rather small at the same time depending on where your looking, its that leg, the one in full view, because its over the highway and shown to be in contrast to the highway it looks small as the highway is rather big and looks close, his mouth is taking a bite out of the tall building again making him look huge and the tank in his had looks like a toy tank because of this scale issue. If his leg were to be moved to behind the highway along with the other leg, add some more haze to the lower areas of the robot to really make it look huge and solve the confusion.
I'd have to agree with the critiquer, your left leg is REALLY screwed up. I mean, head is clearly large enough to bash in a skyscraper, but the foot is only the size of a minivan?! That seems so incredibly unlikely, even George W. Bush admitted it was unlikely.