First off sorry about the lack of an image but I know some of the folks at DeviantArt don't like there stock going of site.
Here's the link to the image. http://fav.me/d6fvh3d

I'm curious as to whether the perspective looks okay or does the helicopter look too big. Also I'm tearing my hair out with the missile explosion, I just can't find a way to make it look any good. One of the problems is that I've no idea how the blast should spread out when it hits something that is pretty much indestructible. Any other thoughts and comment on any aspect of the picture will be much appreciated.

I like the general layout. As for sizes, I have no idea how big Godzilla is supposed to be, or how far the copter is from the monster. The crashed helicopter seems to be sized correctly. As for the blast, I think there could be more broken up particles or rays where they hit the monster.

this is very well done, Caz !

i think the explosion is good as it is

what i find a bit odd, is that the sea appears to be very shallow, because only Godzilla`s foot is submerged
also the timing of the image may not make sense if you think about it
thats because of the crashed copter
i know you added it for dramatic reasons
but if you think longer about it, how can it be: its about to fall into the water, while Godzilla is already looking at the other helicopter and getting a rocket in the chest ?

maybe it would have been better if Godzilla would hold part of the heli in its claw

the piece would work without the crashing helicopter, just as good, but i understand why you added it

as i said, very good work overall
i love this kind of stuff !

I like the overall scene! As for your concerns, I think the explosion is too dark, and too red. Google "missile impact", and there are a few good references in the image search. As long as you don't have too much flying debris, we should believe the monster is indestructible.

One thing I noticed is the light seems to be coming from multiple directions. There's a strong source shining from the left, and a weak source shining from either behind the "camera" in the background, or from the right. I see the background was composed by merging a few different cities. Maybe flip a few of the segments horizontally?

Very good composition/manipulation.
I just do not understand where the light over Godzilla comes. It could be being lit from the front, but in that way I think it should illuminate the back of the chopper too.
Just that, and maybe I'm wrong. So an excellent job you have done!

caz: really great job!! i thought of the timeline too, just like esper, but maybe it doens't matter that much. i do think it's a good idea to think through where the lightsources are, though, it's a little bit undecided at the moment. the general composition is great, though and i thought the explosion looked fine.

Thanks for all the comments they're really useful.
The lighting is probably the biggest problem I've got with this image. The stock picture of Godzilla has a strong light source which is mostly across his chest and legs, I guess it comes from a flash or some such at the time when it was taken. I've tried toning it down or lightening the back and tail areas but so far nothing looks quite right. I guess it comes down to either making the big guy lighter in the shadowed areas or toning down the light areas and then run the risk of losing detail from the scaly body. Tough call that one. I need to try something though as the light source from behind the buildings indicates a sun set or burning city, probably the latter with the big guy on the rampage, and the light source higher up in the sky would seem to place the sun over to the left, I'll try flipping that one and see how it looks. Also I'm going to move the tail section of the crashed helicopter so that it's in the claw, not sure how it will look but it's certainly worth a try.
Thanks for all the hints on this, the perceptions of others is always invaluable.