Portmeirion. Is it worth a visit?

It's pretty underwhelming to be honest, maybe if your planning on spending time in and around that area, it's worth popping there for half a day. But I wouldn't make it the main focus of your trip.

Oh and it takes about 6 hours to get there via train from london.

Figured as much. Hadn't planned on staying there for more than a day: pop in, maybe take a few pictures and get the shit out of Dodge. Spend the rest of the time somewhere else.