I remember those first time around :oops: as being stonking guitars. At the time (ie late 70's) I think it was the SG series which really scared the wotsit out of Gibson - whose QC was not the highest at that time - and which led to the US manufacturers trying to put the Japanese out of the business through all the lawsuits. Obviously, they couldn't touch the Yam SG series because they weren't a copy - which made them all the better.
I never owned one - pocket money wouldn't stretch to one back then! - but did play a couple and have very good memories of them. Rock solid build, sustain slightly longer than forever, good range of sounds with the coil taps.
Originals in decent condition will fetch £600+ on evilBay, and there aren't many around without scratches, dents, dings and tarnishing. Paintwork tends to go cloudy too. There's an eBayer based in Japan who lists them quite regularly (eBay name: Chingo-something) - I've got stuff from him and his service is excellent.
Heavy guitars too :D
