It is awful. I hope one day it's as good as pgAdmin3, but I'm not hopeful. It's great to develop it in the same way as postgresql because that's how the developers are used to working, but it would really benefit from a more open development model using github or gitlab. I don't understand why they chose their tooling for pgAdmin4, but I'm sure it must be buried in the mailing lists somewhere...

Thankfully BigSQL are still updating pgadmin3 to work with postgresql 10: https://www.openscg.com/bigsql/pgadmin3/