The patch includes a some work with the chat interface, more character slots (24 to be exact), stability fixes, and other changes to make the play experience better.
They've also discovered what's causing the "Invisible Party Member" bug, but didn't discover it in time to make the patch.
Patch 0.5 also brings an end to the Guy Fawkes event.
IMPORTANT! The patch implimentation is expected to cause server outages between 9:00am PST and 11:00am PST today (11/20).
Visit the official site for the full patch notes:
www.hellgatelondon.com