My last one? Bulletstorm demo. One person, five skillshots, not to mention all of the other kills I garnered from the explosion.
I believe the skillshots were 'Sadist', 'Misfire', 'Toxic Love', 'Bullet Kick' and 'Voodoo Doll'. I then proceeded to get a time of 3:14, and 9466 points. That game is so fun.
Other memorable "Hell Yeah!" moments include beating MGS4 on The Boss Extreme, beating Unlimited Hazama for the first time (god that took ages), beating Seth on Hardest mode for the first time (I used Cammy).
Another one was in Fallout 3. I have a nigh-on unstoppable character, having beaten the game and all the expansions, I walk into Evergreen Mills with nothing but the Vengence, the Gauss Rifle, a shitload of microfusion cells, electron energy packs, and my Winterised-T51b armor, and proceed to clear out the place, including the Super Mutant Behemoth, without dropping to half health. I felt immortal