I've been playing and grinding the RN cruiser line hard since it was released (I now have a Fuji). Apart from tier II-IV my games have almost alway been fun. I think the RN line is excellent. Especially from Leander and up. If you're used to a playstyle though, it really requires a shift in mindset to play them. But once you do they are very good ships.
I'm not British though. And I think our resident British playerbase expected the hail of the new royal navy ship line to be a paradigm shift of World of Warships. E-Brittania rule the waves sort of thing. No, just no. Like everything take the time to master it, before you spew out conclusions on how terrible the ships are. Having 30 games or less don't give you the insight to write it off entirely, like it looks 90% of the posters ITT does.
And the Belfast is made of pure awesome sauce. A bit OP. Borderline ridiculous. It shits all over the Flint which is the closest resemblance in game (but apart from them both being CL's they are very different).