I've had some decent fish up there, albeit not consistently.
As always with the upper Don the weather is the catalyst for sport, especially on dry fly, but you want a few days of half-way settled conditions for it to be more than just a slog working your way through holding water with nymphs and streamers. The upside is there's lots of water to cover, the downside is that the fishing can be 'thin'.
The section below where the Corriehoul Burn joins the Don (Look for the long pool below the graveyard at Goodbrand & Ross in particular) is usually productive and unless much has changed the next mile or so below is all good water. Certainly where I would choose to start any upper river exploration in the early season.
H