I think the pace of this movie may be the real issue. Where 2014 was a slow build up, this movie dove straight into the deep end and didn't slow down at all. We open with an action sequence with Mothra, fairly quickly move to Antartica, jump over to Mexico, from there it's a mix of Godzilla's ancient temple, DC and Boston and then straight to the Boston finale.
The oxygen destroyer makes an appearance but could have been a point for some solid drama and slown the film down a bit without getting boring. This could have also been woven into elaborated drama between Monarch and the government.
Build upon those and add more to the story with the eco terrorists and particularly Charles Dance and you'd have more meat in the movie which as is feels more like a 100mph roller coaster that never lets up. It's like 2 extremes, 2014 was criticized for a number of things, this movie goes 180 on most of those but even that's not the best case scenario, the best falls somewhere between the two.