I was watching some trailers for Modern Warfare 2 and began reminiscing about the original Modern Warfare's singleplayer campaign. It took me completely by surprise with how well it was made... after the opening scene/credits I was hooked. The cutscenes and storyline were so well done, and how well they were integrated with the gameplay had me more enamoured than I've ever remembered being in a FPS campaign (yes, even Half Life).
With all of the unique surprises this game, this scene took the cake. I don't think I've ever been as solemn playing a game as I was at the end of "Shock and Awe".