I liked it that it used maple syrup as the sweetener. My dark choc was quite bitter so definitely needed the maple for my taste. So I think the answer would partly depend upon dark choc used. You could always make it without the maple syrup, then taste test & add if required (can always add in, but can't take it out).
I don't think it was a super sweet syrup, if I have second thoughts after my hot drink in the morning I'll let you know.