This is a great title for a movie, and it's the only thing I call it. Adding "Godzilla vs" to it makes it far more generic than it needs to be. Monster Zero is amazingly mysterious. In fact, I passed it up one day because I didn't know what it was about. Never made that mistake again! I don't even have to add that Toho's "official" title for this movie is one of their dumbest decisions ever. PS, yes you do get the bonus WAR OF THE GARGANTUAS trailer, since I can't find a separate one for MZ.
The first time I did see this was on a school night, in a two hour slot, 8-10 PM. I was a little surprised at the lack of monster action in the middle, but as has been noted by many other people, the storyline carries it along very well. It's really a good movie, and the Xians are cool villains. You almost feel a LITTLE sorry for them. Too bad they were so arrogant. How much water could that little asteroid have needed?