Fantastic movie, go see it if you like Godzilla. Suffering more from release timing than from anything else, it's being lashed by critics who're too shallow and focused on celebrity cameos and humans (as usual) that they fail to see the symbolism in it, or simply fail to accept that it's beyond them.
Godzilla: King of the Monsters pays homage to, and incorporates elements of, all previous incarnations of the Godzilla franchise. Just as its predecessor did. The campiness of the 'science' given in Showa, the serious approach of Heisei and X, and the symbolism of the original 54 film. Godzilla: King of the Monsters is a fun story, exciting at the right pace, and carries deep themes about nature and the role humans play in it. With a world wracked by the effects of pollution and global warming, these are important themes to consider, and personifying these things in the form of kaiju is quite powerful.
I don't like giving spoilers, but I will say that, if you're an old hand in Godzilla, or you're newly into it and want a good place to enter the franchise, this film and its predecessor are the best spots. And if you like it, do make sure to let Warner Bros. know and to push them to not have reshoots of the upcoming sequel, Godzilla vs. King Kong.