I've said numerous times that I'm fine with the premise. I rarely judge these types of films the way people that hate dumb fun films do.
The point had to be made that in our immediate real world there are other options. Amassing many many gallons of real world toxins that mess with the blood and the nervous system(see snake venom) of carbon based animals and even adding synthetic stuff to the brew would be alot more feasible then a functional Megazord imo. If they are bent on hardware then I say go smaller rather than bigger, if this is a world where they have the tech to make a megazord....
And lastly what seems like the most obvious option, attack the creatures form the inside, bomb detonations my do squat in the face of a hard scaly surface but it's a different story on the inside.
It's just a movie, funny how many times I've had to say that to the people that think sending oil drillers to blow up an comet is dumb. I do find it interesting to see which films fanboys choose to defend though.
I for one can't wait to see it, it's the only movie I have left to look forward to this season.