Plot-wise . . .
I think this might be my favorite Godzilla flick thus far (granted I haven't watched even half of them yet, though I grew up on them). I mainly like it because, aside from the later films, this plot is simple and acceptable. The only part I can really point out not liking is when Godzilla and Ebirah play catch with the giant boulder.
Otherwise, everything pretty much makes sense. It is quite illogical that Godzilla would reside on the one island in trouble, but whatever. I also really liked the depiction of Mothra as it should be depicted . . . praised, surrounded by believers, and majestic. Thumbs up!