The hardest question you could possibly ask me is what is my favorite of anything, especially with such a broad category as "favorite video game." If the question was what is my favorite video game under the genre of shooter I might be able to say Quake III Arena, maybe Action/Adventure I would pick The Legend of Zelda: A Link To The Past, or maybe real time strategy I could say the StarCraft series. The point being that I cannot chose simply one game out of all the rest.
But for the sake of a college degree I will. StarCraft. Don't ask me which one since I love the original and it's expansion and am still entrenched in the new unfinished trilogy. The StarCraft series is my addiction, it has an amazing and expansive storyline that's engaging and versatile. The storyline is only one piece, the online multiplayer is nearly flawless and to have both aspects shine so brilliantly in todays gaming market is astounding.