I've already seen Metallica live, and while they were better than I expected, I don't feel like I absolutely must see them again so soon.
So, basically, this tour stands out simply because I have yet to see Megadeth live, and to hopefully see Metallica play more than jsut Creeping Death off Ride the Lightning (which will probably never happen).
I like Anthrax too, but not as much as the others.
And as for Slayer, I'd probably only be interested in seeing them play "Raining Blood", and then leave, since I've never really cared for them.