While it isn't exactly a pleasant tool to use, it's not like it's totally broken either. I've used other similar software that was much worse to use than pgAdmin 4 is.
It's slightly better than pgAdmin 3 in some ways, but it's also worse in other ways. Overall, it's mediocre. That might be the underlying problem: it doesn't live up to the high expectations that the rest of the PostgreSQL ecosystem tends to set.
If I had to give it a grade, I'd say it's a B- or a C+. It could be a lot worse, but it could also be a lot better.