The fourth and most highly regarded Godzilla sequel, one which pretty much deserves almost all the acclaim it gets. Yes, there is a bit of a problem with the ending (I've gone over that elsewhere) but overall this is a pretty awesome movie. I'd say it was actually the best Godzilla movie ever. Yes, better than the first one. There, I said it.
Of course, the US title is very misleading. The posters are great, but you'd never know it was Mothra that Godzilla was going to fight. At least by looking at the ads and the trailer (there's a glimpse of the grubs, but it implies something else is also in the movie). It's a great trailer, though. Would have got me into the theater for sure.