Shadow of the Colossus. I remember the first time I played it it was a demo on a disc from some magazine I picked up. I had no idea about the game but I decided to give it a shot. It was like, OK I'm on a horse, i have to find something, Climb a mountain, this is decent and the graphics are nice. then that first colossus walked out and I was like Hooolllyy Shit!! I have to kill that thing. Climbing the Colossus and killing it for the first time was one of the biggest rushes I've ever gotten from gaming. I must have played that demo 10 or 12 times and I went and bought the game the day it came out. Still one of my favorites.