Just my 2 cents on the Joey/John arguement.
Joey was perfect for Anthrax back when Anthrax's music was more fun than serious. When the music started to get more serious, Joey's voice did not fit it and Bush's did. I really think it took a few albums to really fit Bush into the band, but he really proved how good he is on Volume 8, in my own opinion.
As far as jumping the shark, Anthrax never jumped the shark. If anything, blame the music industry and MTV (god I wish this station never existed) for spoon feeding the entire nation crap like Nirvana and making everyone think that all music was supposed to be from Seattle.