I love the house, But I think if you've got black windowframes, you should go easy on the black inside. But a bit of gentle colour and some soft pattern on furnishings would go a long way to softening it.
I've certainly seen a lot worse.
The dining room table is rather anachronistic, it needs a lovely mahogany oval table that seats 12!
And unless the owners spend all day in the gym, I'd use that fabulous room for something else.