Actually, I'd say Metallica is the only truly world-wide Metal phenomenon these days. Yes, Maiden has been successful in headlining major festivals every summer, but they are much bigger in Europe than in N. America, where they can headline arenas and amphitheaters, but not stadiums.
I'd put them like this:
Metallica: Stadiums
Maiden/Ozzy: Arenas & Amphitheaters
Slayer/Megadeth/Judas Priest: Smaller arenas and package tours
Many of the other classic metal bands will headline theaters and clubs (Testament, Anthrax, etc).
You can throw in a lot of the current popular metal bands in the category of arenas/amphitheaters, often with package tours. Bands like these include Disturbed, 5 Finger Death Punch, Korn, Avenged Sevenfold, etc.
I think this is spot on, and it's exactly how things play out down here. In fact, all of these bands have or will play in their respective tier within a year.
Metallica was able to do Stadiums in the US cause they packaged with Avenged Sevenfold and Volbeat. I'm not trying to diminish them, they are clearly the best ticket seller in this catagory (well actually Guns N Roses are according to billboard).
I don't think this is entirely correct. I think a big part of the draw for Metallica this time around was that it
was a stadium tour, with the massive production that entails. Also, the album was pretty popular. Had they just played their normal
in the round show at AAC I doubt they'd have sold it out. AV7 most likely sold them some tickets, but not enough to be the difference between a stadium and arena show.
Gojira is a good call (and opened for Met a couple of times), Rammstein is also worth mentioning when discussing this hierarchy. They sell better than Maiden here in the states, and while certainly an old, established band, they're still years behind Metallica, Maiden and Ozzy. I think Tool will also continue to tour well beyond those guys, though it'll probably still be the same 18 or so songs.