A triumph of free speech and creative freedom.
I put close to zero credence in reviews due to various spam groups propagating their agenda of awards manipulation and the vast morass that is ignorant, unquestioning public opinion (amongst other things), but I feel compelled to review this flash despite the almost inherent futility of the act.
First and foremost, I commend you on how you conveyed the events of the massacre. People playing the game had to follow a rough parallel of the final day of Cho Seung-Hui's life to advance the story. You included some popular conjecture of Cho's motives that has been circulating around the internet into this storyline, but that definitely fits the bill stylistically considering the various internet slang and memes referenced throughout.
While the pixel graphics were adequate the sound is where you really excelled. People familiar with the case will instantly recognize the song "Shine" by Collective Soul. Cho listened to this song compulsively and even inscribed the lyrics on a dorm wall. During the second phase of the game that includes a stealth-based theme, Mr. Brownstone is played. This is a reference to the name of a disturbing play written by Cho. At Norris Hall, where the main massacre takes place, there are many witty aphorisms you included that Cho seemingly thinks to himself during the massacre. Some of these include the extent of the damage he inflicts, the killing of false idols (which he mentions in his manifesto), and of course the Zerg "bullet" rush. A particularly interesting quip is intoned after killing Professor Liviu Librescu.
All in all, this was a decent game rife with entertaining witticisms that demonstrate this was all done in jest, with no real malicious intent. It was unique and for the most part, well thought out. Sure, some will infer that this was made in poor taste. Maybe a disclaimer asserting sympathies to anyone involved could have been handy to help people generally acquiesce, while simultaneously letting your true intent be conveyed. This deserves recognition, but I fear it will be the wrong type.