First, it takes place in an alternate universe where bombs, missiles, and artillery were never invented. Quite possibly explosives in general were never invented, aside from extremely low-yield nuclear bombs the size of houses with the explosive output of a large bag of fertilizer.
Also, the coefficient of friction in the atmosphere is much higher than on earth -- jet fighters have to swoop into melee range to use their guns, which makes them completely ineffective, and falling from 30,000 feet results in a robot nearly burning up on 're-entry'. But at least the reduced terminal velocity means that it can stick the landing without serious damage!
So... yeah. The technology is seriously wonky. Did I mention the robots are controlled by giant levers and buttons and switches but the pilots have to undergo a 'neural link' with them anyway? ONE OR THE OTHER.
Oh, and the Pacific Ocean is about ten miles across and maybe 500 feet deep.
But none of that really bothered me, and the subplot with the ridiculously stupid scientist was handled well -- you were actually still rooting for him even *after* he got almost everyone killed.
The only things that really annoyed me were (a) the complete ineffectiveness of the robots other than Gipsy Danger -- they spent longer talking up those guys than they survived in their only on-screen combat. And (b) some of the mental-link tearjerker stuff came off as jerking of a completely different sort and, worse, was kind of boring.
But, yeah. It's a giant monster movie, and the giant monsters (especially the one with the tail) are interesting even if the robots (that survive more than ten seconds) are kind of boring.