There's 28 films in the Godzilla franchise sans G.I.N.O. 1998. I haven't watched them all and I'm not going to bother to. At least not for awhile, but I'll pick my top 10 films:
Godzilla - The original film where he was a creature to be feared by all as he was the living embodiment of America's use of nuclear weapons during World War II. It was political message, but people loved seeing a giant monster destroy stuff (the dinosaur version of The Hulk) and he's been a cult icon ever since. Watch the Japanese version. Its better than the American version and has a lot more footage. Godzilla dies at the end of this film so every movie you see him in after this is actually a second Godzilla.
King Kong Vs. Godzilla - Following the footsteps of Frankenstein Vs. The Wolf Man, two monsters would fight each other here. King Kong has now grown to the size of a skyscraper for some reason takes on the large lizard in this battle of epic porportions. There was a decades old rumor that Godzilla wins in the Japanese version of the film. That is false.
Godzilla Vs. Mothra - Mothra, who would become a staple character in the series, makes her debut here to protect her egg from Godzilla, who was still a bully at this time.
Ghidorah - He is a three headed dragon from Venus who arrives on Earth to destroy all life and Godzilla's top villain. He is so strong that it takes the team of Godzilla, Mothra, and Rodan (a giant pterodactyl and Godzilla's buddy) to defeat him. This was the film that turned Godzilla from a bad guy into a good guy.
Destroy All Monsters - This was basically a battle royal with Godzilla fighting all his past enemies because of evil aliens from Planet X that want to take over the Earth (a plot that would be re-used in the sequels time and time again) all in one film where at the end, he establishes himself as The King Of Monsters.
Godzilla's Revenge - A little boy is being picked on by bullies and imagines himself going to Monster Island where he befriends Manilla, Godzilla's son. (Yes, Godzilla has a kid! He laid an egg and hatched in a few films prior to this one.) Godzilla teaches Manilla how to get stronger and using his powers in order to fight off other monsters. This encourages the boy to have courage in the real world and fight the kids picking on him as well as two bank robbers. A lot of fans hated this film because it was campy, but I liked the fact it didn't take itself seriously. After so many serious films that included death and destruction, it was a nice change of pace.
Godzilla Vs. Megalon - A giant cockroach that can spit bombs of his mouth and drills underground is sent by people living underwater to destroy the world, but becomes engaged in battle with Jet Jaguar (Ultraman, another popular Japanese superhero, knockoff who can change his size like Ant-Man). The battle is back and forth until Gigan, a foe of Godzilla from the previous movie, arrives and the two evil monsters jump the robot until Godzilla comes to his rescue and thus you have yourselves...a tag team match!
Godzilla Vs. Mechagodzilla - This film introduces one of his greatest enemies, a robotic version of himself created by mankind to destroy him. They would battle each other in many films to follow after this.
Godzilla 1985 - It basically a remake of the original film, but works well in its own right. Because of legalities, it has yet to be released on DVD or Blu-Ray, but if you can watch it on VHS, its totally worth it.
Godzilla Vs. Destoroyah - He fights a mutated crab lizard who gets stronger throughout the film. It turns out Godzilla is dying in this as his body cannot handle radioactive powers. Very sad to watch his demise and his son, Manilla, takes his place at the end.
Honorable mentions:
Godzilla Vs. Hedorah - He's basically Captain Planet in this as he has to fight an evil blob creature that feeds off the world's smog pollution.
Godzilla 2000 - Scientists find out that Manilla (or technically Godzilla III now) has the ability to heal any damage done to his skin (ala Wolverine). He fights an giant evil alien in the shape of a UFO who wants to steal his DNA.
I've ruined myself of thy movie.
