Having one right now. No, you don't expect gold from McDonald's, but it's a half-block from me and the nearest place to get something like this. And I had an urge for this sort of drink, so I figured I'd try one.

Verdict?
For $3.20,
no. It's tasty enough, not too heavy on the ice (as they are with their sweet tea), a bit too much chocolate for my taste but not overwhelming, the coffee part is pretty good. But for $3.20, no. It's a 16 oz. cup for the medium, which is $2.99 plus tax. That's just not enough goods for the money. For $1.99 I might vote different, but for $3 I can get a heaping 32 oz sweet tea (though its mostly ice), a chicken sandwich and fries.
So, pretty good -- though not as good as you'd get from a quality place, obviously, or even as good as Dunkin Donuts -- but the price it too high.
HINT: On Monday's, you can get 8 oz samples for free.