I think that movie would not have gotten the bad rep it has if they had not mutated a salamander and then called it Godzilla. It's definitely not Godzilla, but I wouldn't call it the worst movie I've ever seen by any stretch.
It's not technically the worst movie I've ever seen, of course - I have seen stuff like Sharknado and whatnot - but when factoring in the budget and intent behind it, then yeah it is the worst. Sharknado is supposed to be a joke, you're not supposed to take it seriously and you know it's shovelware made as cheaply as possible. It does fail to be entertaining even on those terms, yeah, but it's still just a joke film.
Godzilla, though? That was a big ass Hollywood blockbuster. It had a massive budget and most certainly had the intent of being an entertaining flick. I watched it once as a kid, thought I didn't remember anything and decided to give it a go again after growing up to see what the fuss was all about. I went in expecting a bad take on Godzilla, but an enjoyable movie all things considered, even if it was in a dumb fun kind of way. Instead, what I got was a 2-hour cringefest of atrocious acting, a hilariously bad script where basically every plot point is extremely unsatisfying, and a feeling that what was largely supposed to be a dumb fun movie, ended up just being dumb unfun. All those things are where it fails as a movie in general. Where it fails as a Godzilla movie specifically is everything else, and it's also amazing how bad they manage to fuck that up - see, I'm no big Godzilla fan here, but even I felt personally offended by their take on the character. It all just sucked to a degree I had never seen a Hollywood movie suck.
It basically is Sharknado, but with a massive budget and studio behind it. It doesn't have an excuse for being trash.