Not to echo what's already been said too much, but give the show a chance before criticizing it. It does pretty much the exact oposite of what you described.The problem I have with this is it just further exasperates the problem we are currently having with the kitchification of certain genres of metal, like death metal.
So her job sucks so she kareokes to death metal?
It's 'funny' because it's a super deformed super cute cartoon cat or fox or whatever, but death metal is scary for reasons we have no idea, nor can we remember how or why this imagery is a thing, it's just, you know, that thing you see, the news shows it, metal is all scary and demons and blood, because they like war and murder and corporate greed, cause their evil right? Thats what metals for right? I mean it must be, thats why it looks like that and what the media says. But the show looks cute and cuddly! ha ha!!! Low hanging Juxtaposition! Everybody laugh!!!
Metal isn't used as a joke or a punchline here. It's a coping mechanism; and quite frankly one that is totally realistic. One of the biggest appeals of metal for me has always been that I can sing along with it and feel a genuine anxiety/tension release while I'm doing it. The same applies here. It's her way of balancing out after a day of being underappreciated and essentially hating what her life's become.
That said, the metal used is about as baseline as it gets. I don't know what bands you like (though based on responses in some passed threads, I gather that you've listened to Sabaton at the very least) but I'd absolutely say don't go into this expecting music that'll blow you away. Metalocalypse is still the best show for that sort of thing...