Theres alot of metal bands here, that part you got right. Otherwise Swedes arent maybe the most easygoing people, but almost all speaks english well so you wont need swedish for a visit. There are a bunch of metal festivals etc, if you want to plan your trip with some music. Otherwise it depends on what you want to see, most tourists go to Stockholm or Göteborg I guess, so thats a good place to start.
Some vocabulary for you :)
Fika - Mid day snack, usually alot of sweet stuff
Dubbelkagge - Double bass drum
Hårdrock - Heavy metal