Indeed, the scale really is mind bending. If you start in EL Cap meadow and hike towards the base, you'll notice that the base keeps being farther away than you thought it was because the height is much greater than what you thought. This is even more pronounced when approaching the South face of Half Dome (from the South) as there are no tree to obscure the view. Also, if it's your first visit to the park, I highly recommend entering on Highway 41 (as opposed to 120). You don't really see anything until you pass through the Wawona tunnel, and then you are greeted with the amazing Wawona view [1]

http://en.m.wikipedia.org/wiki/Tunnel_View