Id say Redcliffe is what really got me into the game.
First playthrough:
Second playthrough:
To me, the small thing such as a single dialogue line of a person who may or may not be directly involved can change the outcome of a situation I thought this was an excellent touch.
Of course, doing more reading on DA, it seems Ive missed a few things concerning Alistar and Morrigan I think would be neat to play with, so I gotta go through and tinker with that some.