I live in the Galloway area and love the walking. The Rhinns of Kell is a long, tiring ridge walk( no hairy cliff stuff tho- large rounded hills) with stunning views across the Galloway range, over to Arran, Ayrshire and down to the Lake District. For such great walking, it is usually quiet. Apart from the Merrick, which is often busy, the other hills are usually empty. I have gone all day at times and never met another walker.
There is great mountain biking in Glentrool and around Newton Stewart which is bringing people and money to the area.
Galloway is an under-rated area with potential long days and some strenuous hills. Well worth a visit.