A van Gogh painting swept me away. Behind the thick swirly impressionist strokes he had captured everything in a scene as if it were a photograph, complete with shallow depth-of-field such that if I looked at just the right spot, in my peripheral vision, the paint vanished and I was transported there, seeing it as he saw it. It was cold and ... well I guess dude needed glasses. :)
It's a winter scene near the sunflowers in the van Gogh museum in Amsterdam.
I suppose it changed me as a demonstration of just how compelling a piece of art could be.