The US has a stack of bands that I'd claim are good, in a variety of genres too. Plenty of death metal (the whole Florida scene, for starters), black metal (Xasthur, Leviathan, Weakling...), doom (While Heaven Wept, Morgion...), thrash (Death Angel, Slayer of course...), the thrashy/power stuff like Nevermore and Iced Earth. And of course, these "NWOAHM" bands like God Forbid etc (although personally, I'm not interested in this, but there are plenty of people who'd call it good). It would be pretty ignorant to say that there's nothing in America.