Lost Planet 2. Headshots give an incredibly satisfying 'PTCHT' noise. Though, usually sniping battles come down to using them as aggressive megaweapons, meaning fighting about 10 feet away from each other with sniper rifles, rolling and jumping back and forth taking shots. And damn is it fun!
I remember fighting someone one on one in a narrow corridor. We were taking shots, back and forth, him with a plasma rifle and me with a 5 shot burst close quarters sniper. We both hid on the outside of the corridor behind a wall. He came out from behind his wall and I made my move. I went into a roll from behind my wall, aimed, took a shot and popped all five of my bullets into his frickin' face. It was very satisfying.