I watched both Ghidrah and Monster Zero today. Here are my thoughts on the former.
Ghidrah, The Three Headed Monster has a great story; aliens, international incidents, and giant monsters all wrapped into one. It's very clever, and I like the ominous tone the movie tries to adopt.
However, a good story still needs to be executed properly; unfortunately, the presentation in Ghidrah is somewhat lacking. The pacing seems a little slow, and the balance between the different plots isn't handled as well as it should have been: I think it focuses too much on the political assassination plot and not enough on the IMPENDING DOOM AND DESTRUCTION AT THE CLAWS OF THREE GIANT MONSTERS. Granted, Godzilla, Rodan, and Ghidorah all have impressive intros, but then it takes a long time before they actually start doing stuff -- and once again, the menace these monsters present seems underplayed.
On to the action. This is, of course, what we want to see most, but once again the film gives a mixed performance. There are some great shots (I don't think I need to say which ones), but there are a lot of bad ones as well. The mediocre-looking puppets are greatly overused, and shifting scenes from puppets to suits is a bit jarring. Once everyone gangs up on Ghidorah, pretty much everything improves.
Like previous viewings, this one was the dubbed version - and I really realized this time how bad the dub is. You can easily imagine these voice actors reading their lines straight off the script, and what's more, some of them don't even sound like they know English well. I really need to see this movie in Japanese, because the dub greatly detracts from the viewing experience.
Overall, Ghidrah is still a good movie, but I can't call this one of the best. 5/10.
(EDIT: would someone bump the thread for ASTRO-MONSTER? I was the last one to post there.)