Just got back home from the theater, I loved EVERY SECOND of this!
I give it a solid A. I liked it more than G'14 (which I liked quite a lot), but I'm undecided whether or not I liked it more than Kong: Skull Island. Will need to digest it more.
1. Of the human cast: Kyle Chandler, Vera Farmiga, Millie Bobby Brown, Charles Dance, Ken Watanabe, and Sally Hawkins are wonderful as expected. Bradley Whitford is the comic relief and REALLY funny IMO. ^_^
2. Of the monster cast: everybody gets a moment to shine, though I think everyone when they see it will agree that maybe a little more for Mothra couldn't have hurt. The audience I was with seemed to really love all of them though, a lot of cheering for Godzilla, Rodan, and Mothra.
3. If you were disappointed about "cutting away" in G14, I think you'll be satisfied here. The intercuts between human and monster action is more like we're used to in Toho films, with long stretches with the monsters (of which we get a LOT), scenes with the monster action in the background (or the humans literally trapped in the middle of it), and a handful of human/kaiju interaction scenes (all of which I felt were handled very well). While G'14 was like Godzilla through the lens of an American disaster movie, KOTM is like Godzilla through the lens of a Marvel-style Action-Adventure event film.
4. THE MUSIC. Godzilla and Mothra's themes are very prominent, immediately recognizable. There were a couple of other tracks that sounded like they could be Ifukube-based, but I wasn't sure...in particular, I thought I heard at least a little bit of Rodan's theme when he first emerges from the volcano. What made me smile just was wide, though, was the track from G'54 that plays when the fighter jets attack Godzilla is played here when the military attacks Ghidorah.
5. The credits are done in the style of the MonsterVerse openings (with the news clippings) and gives some pretty big hints as to where they may be going with these films. In particular, I think it does a pretty decent job setting up for Godzilla vs. Kong and explaining why that's the story that comes next. I've no idea where they're going with that Post-Credit scene though (yes, there is one).