I actually think the script for GvKG is pretty good; that and the music. It's everywhere else that the film falls short. Kazuki Omori's direction definitely isn't as tight here as it was in GvB, and even then I'm of the opinion he was a better writer than director. Yoshio Tsuchiya aside, the cast does nothing for me. The effects work is hit and miss, with more glaring misses, setting an unfortunate trend that the Heisei series never escaped. All the M-11 stuff and the American actors in general are pretty cringe.
The script is pretty solid, though. Lots of ambitious ideas, even if they're not all executed perfectly onscreen. I used to hate time travel but I've been warming to it recently, and it's softened my former disdain for GvKG. Now, I wouldn't call it one of the all-time great Godzilla scripts but I certainly wouldn't throw it in the same dumpster as GvSG.