At this stage of the year its leaves are usually very "autumny". They fade from deep purple to an orange-tinted russet colour, in which the ribs and veins are very prominent - like this:
Photo from 2011
However, this year things are very different. Some of the leaves have just gone a horrible brown:
That doesn't look to me like "Autumn colours". That looks dead.
Even some of the less brown leaves are curling up, which is not normal.
Not all the leaves are affected (yet), but even the best of them have a dull matt look, whereas I would normally expect them to be quite shiny still.
I have no idea what might be the cause of this. Possibly insufficient moisture, although big shrubs like this one normally tolerate much worse conditions than we have had recently. I know that September has been warmer and drier than usual, but nothing too dramatic. I rather suspect that the Cotinus has been struck down by a disease.
Since the leaves would be dropping off anyway, I don't think there is much I can do apart from wait until next Spring and see if it revives. I hope it does, because I love that tree!