Returning after a year
Here’s a great video that shows what changes you’ll see right away (applies to everyone)
http://www.youtube.com/watch?v=Ce_dvXJercI
And another video that highlights changes to WvW
http://www.youtube.com/watch?v=eUfV3OBLyc8
You can see the release splash pages here:
https://www.guildwars2.com/en/the-game/releases/
And here is a searchable patch notes:
http://gw2patchnotesearch.david-reess.de/
Necros are in a much better place than they used to be. I have a blast on my necro. Warriors are still OP according to most people. Mesmers do fine in PvP but there are plenty of other viable options now.
The events you’re seeing are part of what’s called the Living World, 2 week updates, each of which comes with its own set of achievements and a meta achievement that you can complete for some sort of reward. Some people like it and some people don’t.
Sometime the Living World leaves things behind (like a new dungeon path or a new dynamic event) but often parts are removed from it.