I'm interested to hear what are the biggest metal bands in different country. Since Iron Maiden and Metallica are big everywhere, you don't need to mention them. I'm neither that interested in all alternative metal bands. In Sweden, where I come from, the biggest are In Flames, Hammerfall (both have scored no 1 on swedish album chart), Nightwish and Sabaton (scored no 2). There are a lot of bands who have scored top 5 in Sweden.
biggest Portuguese band with Moonspell? Never even heard of it (not that would be definitive as to how big the band is) but the band isn't even featured on Metal-Archives.
Inside Portugal, yes. They are not popular outside in part because most of the songs are in portuguese.
Similar case is our greatest rock band Xutos e Pontapés, popular in Portugal and known in Brazil.