Rumour has it these changes are here to stay (well the logo on the login screen surely must change slightly). The weekend event (not yet started) just allows the new classes (Ritualist & Assassin) to be available for PvP only over the weekend.
The changes I've seen so far :-
You may notice some yellow or purple triangles on your skill icons.
These represent the fact that the skill is an enchantment or a hex (curse).
Getting to the Guild Hall seems now to require you to press 'G' and then the 'Guild Hall' Button.
There appear to be FOUR PvP areas now, which are dotted close around the Guild Hall.
They all look different to the way they did before.
1) Great temple of Balthazar (NEW)
Lots of training bits here like different strength armour to hack, testing arrow range, suffering conditions, understanding 'adjascent/nearby/in the area' etc. There is a zone entrance to Random Arenas.
2) Random Arenas
Replacement for Competition Arenas.
3) Team Arenas
Replacement for old Team Arenas
4) Heroes Ascent (NEW)
Replacement for Tomb of the Primaevil Kings (HoH)
I've heard rumours that the Underworld is now the old HoH maps filled with monsters.
PvE characters who want to PvP may have to advance through the PvP areas. They may not all be immediately available. That's how it seems so far anyway.
There is a ship icon beneath Lions Arch which lets you travel to the first of these - Great Temple of Balthazar.
Right. Enough nosing around. I should go play some RA PvP.