In reply to Tim_C7:
Tim, much of the advice above is on the money! I lived for three glorious years in Dalmellington (a grand spot despite it's reputation ......... the view from my bedroom included the NE aspects of the Merrick!) and explored all corners of Galloway.
For me the pure essence of the Galloway Hills is the Dungeon range (Mullwharchar,Dungeon Hill, Craignairny and Craignow)from the roadhead at Loch Doon (excusing the neds campsites by the loch)and variations of the traverse of the Rhinns of Kells (for the best coverage I always favoured starting from Forest Logde in Glenkens but the ascent of Corserine by following the Gala Lane from Loch Doon and taking in the northern summits as far as the Coran of Portmack and the Black Craig is another cracking route).
For a weekend out in the hills I often walked from Loch Doon via the Dungeon Range, spending a night beneath a specific boulder by Loch Enoch (everyone once in their lifes should be awoken by Loch Enoch by Red Deer stags barking) and returning by the Awful Hand (the Merrick, Kirrereoch Hill, Tarfessock and Shalloch on Minnoch)
Another underlooked route (except in Ken Wilson/Richard Gilbert's Wild Walks) is the ascent of the Cairnsmore of Carsphairn (for me the best route is via the Green Well of Scotland, Dunool, the Black Shoulder and taking in Beninner). I am one of the lucky ones that recall views from its summit that were not polluted by windfarms (in those days the regimented ranks of spruce was enough!)
As a complete aside; any one like me that has fallen in love with this magnificent area of wild beauty; have a root about your local library for a copy of Robin Ade's "Fisher in the Hills; a Season in Galloway" IMHO it is the best and most important work about Scottish game angling; but more importantly it is by a country mile the best written description of these hills and its magnificent landscape, flora and fauna