Whenever I ask that question I get either two responses. A.) I haven't seen XGB or B.) I don't like XGB. I actually like XGB and do consider it canon because there are quite a few reference to RGB and there were even some ghosts that appeared in XGB that were originally in RGB like the Grundel. They even had an episode where the original boys in gray are back in the saddle.
I also consider the Ghostbusters game for PS3 and 360 the 3rd movie. Personally my trilogy is complete as far as a 3rd movie goes.
So discuss and ask anything Ghostbusters related.
