I've stayed in Doubletree properties nicer than any Hilton, and I've stayed in Doubletree properties that were abysmal. Most are somewhere in between.
But for me, when I see "Doubletree" I say "double check." Double check the reviews, the photos. Then I can make a better decision.
Consistency is really the biggest problem with Hilton properties. HGI is about the only brand that really IS super consistent.