Well the RG620 has undergone a few changes since the model that was available in the late 90's. It's been relaunched and has a few new features.
Firstly it's now got the thicker Ultra neck profile, more strat like than the Super Wizard found on the previous incarnation. It's also got a three way switch instead of a five way, so the tones are less varied, but easier to access. Both these features are very reminiscent of the old JPM100 model
It comes with the original Edge trem, rather than the Lo-Pro edge, but this is only a very minor difference. But the pickups have been downgraded from the QM series to the V7 and V8 found on most of the mid range RGs, adequate in their own right, but you probably will want to replace them later.
The body is also bound on this newer version and I think that's a big plus, even though I'm not to keen on the colours. Even so it's a great guitar, and just a little different from the previous RG620 or the RG520.
Hope that's been a bit of help.