I never felt like DF has a tone to it. There's no real history to the world. I mean, I know it generates one, but there's absolutely no culture. They worship these random gods, but all you know about their gods are their battle stories. For all their personality, they don't really have ambitions. They don't struggle for power. They just... make stuff. Their whole lives revolve around stuff. Build stuff, mine stuff, ask for stuff, sell stuff, defend their stuff, explore their lost ruins for stuff.
Killing things doesn't make it grim. There's nothing depressing about it. The song isn't particularly happy/creepy either, it's quite neutral.
I think it'd have a tone if the game actually tried to speak to you. Like if the dwarves start carving their bedroom walls with the story of how their brother fought an elephant and was crushed and later on brought back as an undead. Or if they write petitions. Or make temples and shrines to their gods; their chosen deity is even less significant than their favorite food. I heard they do stuff like this, but I never really experience it.
Hoping the upcoming version will give it some kind of tone