After the expansion went live I get frequently kicked out of the game with the message that Guild Wars 2 has encountered a serious error and needs to close, asking me if I want to send a ticket.
I ran GW 2 Repair once and this has rarely, if ever, happened prior to HoT. This happens every time I try to play, so the game has become barely playable for me. Seems to be more frequent in crowded areas.