This post contains massive spoilers. Don't read if you haven't seen the mentioned film and still want to see it.
Also I'd like to point out that written content applies only in this film's universe and is not comparable to other flicks. So statements given here might sound ridiculous to fans of the mainstream and blockbuster film.
Gojira (or Godzilla) vs. King Ghidhora from 1991 is one of the greatest Godzilla films, I think.
You might think that the 18th instalment of the series must be worse than all 17 prequels and I'm not saying that it is the best of all (the original film from 1954 is still the best), but it definitely ranks in my top 5 of Godzilla films. It's the second directed by Kazuki Omori. He already directed Godzilla vs. Biollante, which already had an interesting set up for a Godzilla flick. Unfortunately it wasn't very good in my opinion.
However Godzilla vs. King Ghidhora did a few things right. First of all it gave Godzilla finally some background story and history.
Godzilla fans all over the world must have wondered where Godzilla even came from in the first place. Godzilla used to be a dinosaur who lived on the Bikini Islands in 1944 and as the USA tested the H-Bomb there the dinosaur became Godzilla (you should know that Godzilla's source of power is radiation and nuclear energy so this is a rather consequent back story (I'm not going to discuss the dinosaur in 1944 thing, or else wise I'd need to discuss the whole monsters thing in post modern times...).
SECOND SPOILER WARNING! MAJOR SPOILERS FOLLOW
The second and most important reason why this film is good is because it made Godzilla return as a villain again. Previously (except for the first few instalments) he was famous for saving Japan and even being "friendly" with kids. He was a hero. This time he is the havoc and destruction triggering monster that he used to be in 1954. Kazuki Omori did explain this quite smartly.
Godzilla was still weakened from the anti nuclear bacteria used on him in the previous film and so Japan's government felt quite safe until an UFO from the future appeared over Japan and people from the 23rd century explained to the prime minister that Japan will be no more in 200 years. They said Godzilla would destroy nuclear power plants and radiation leaks and forces Japanese people to leave their country. They came to save Japan and change its history that's why they wanted to travel back to 1944 and teleport the dinosaur to another island so it won't be exposed to radiation and can never transform into Godzilla.
After they did so and left three little cute dragons on Bikini Islands, the people from the future revealed their true intentions. The three cute little dragons became Ghidhora and as one monster it plans to destroy Japan. Fortunately (rather unfortunately though) Japan's government discovered the dinosaur on the island it was teleported to sending a submarine with nuclear missiles to "create" a new Godzilla. Not knowing it was hit by a sunken submarine which carried nuclear weapons a few years ago already it finally caused Godzilla to be even bigger and more vicious.
The previous Godzilla films lacked suspense and thrill, because when Godzilla the hero entered the fight everything usually turned out well. It used to be the typical wrestling procedure. The face (good guy) beats up the heel (bad guy) pretty well in the beginning but gets serious beating in the middle of the fight nearly enduring till the end when the face suddenly regains his will to win and then eventually wins.
In this film everything turned out different. Godzilla defeated Ghidhora relatively fast (yes - the centre head gets torn off once again haha) but continued destroying Japan. People were frightened of him again.
In the end it even needed Cyborg Ghidhora from the future to step in and help.
I also liked the effects of this one. It is visible that they had a lot more budget for this one. Of course the goofy fights and cheap looking monster dresses are still the same, but that's just a trademark of the Godzilla films (CGI effects as for example in Emmerich's Godzilla from 1998 destroyed this. This is by the way (imo) one of the worst films ever made). Also this time the film title doesn't exactly reveal who the villain is (though by reading this you would already know.)
In conclusion there is to say that I highly recommend this flick to anybody who is interested in cool monster films. They are actually rare these days.