Just read all the IMDb reviews of this film (going back years!) so I'm going to confine my posting to things that HAVEN'T previously been mentioned by others. But to briefly recap: this movie is great fun, with a plot that adults as well as kids can find interesting. It definitely hearkens back to the early 1960s 'glory days' in both its epic feel, and its portrayal of Godzilla as a serious menace to humanity.
But you got all that out of the other reviews.
I'm surprised no one else has commented on some rather unique photography techniques used in the SPFX sequences of this picture. I have seen nearly all the Godzilla films, going back to 1954, with the exception of the very recent GMK and Final Wars.
There are several things I found unique about GXM's photography vs nearly every other film in the franchise. This is the only time I have seen a sort of time-delay technique used in showing the monster. At some dramatic moments, the action inexplicably (and artfully) freezes for just a moment. At other times Godzilla's lumbering advance is shown with a surreal technique that makes his movements kind of jerky in a strobe-like effect. Rather than speeding up his movements (which would look ridiculous) this slows action into a 'flash-card' surrealistic style, like a film made with (for example) 12 separate image frames per second, rather than the usual 24.
One thing I didn't care for as much, that is very abundant in this film, is a kind of unrealistic flight effect for Megaguiras. He hangs in the air as if suspended on strings (OK, he is suspended on strings, but they obviously filmed it to emphasize rather than lessen this effect) with wings moving too slowly to be convincing. I don't think this is a "flaw" so much as an intentional artistic choice, but for me it hearkens back to some of the lesser G-films of the 1970s. I prefer the more realistic flight techniques from RODAN (1956). But that is just a personal bias. Unrealistic effects do not equate to bad effects. Too many American reviews of kaiju films make that mistake. Unrealistic is often an artistic choice.
The ending of the movie is also unique and artistic in its own way. No other film from the series ends quite like this, with the dialogue freezing midway through a human dialogue scene. It was a very interesting artistic choice and caught me by surprise. Like the director probably intended, it left me wanting to know what would happen a heartbeat later. But then the credits were rolling.
The big G's suit looks good in this film and his presence is powerfully portrayed. If I had to quibble about anything, I would say that the face lacks animation in many closeups and tends more toward looking frozen and rubbery. Godzilla's face looked much more animated and 'alive' to me in films like 'VS Biolante' or the early 1990s "VS King Ghidora".
There are a number of water effects sequences that look great in GXM. The flooded Tokyo streets, and the big G's spines surfacing out at sea, come immediately to mind. Great entry in the series!