Bioshock was the video game that got me into video games.
Story: Unmatched by any video game that has ever been made. The intensity, the depth, the philosophies (Ayn Rand's free market capitalism and objectivism), and the emotions you experience all play into my opinion. This game could very easily be made into a movie or a novel and be on top of the charts.
Gameplay: Intense and precise shooting action. Gruesome, but not over the top (Quake comes to mind) violence. High paced yet not overwhelming to the point where you feel like it's just not possible (Halo 2 on Legendary comes to mind).
Guns and Plasmids: Awesome of course. I might have liked to see fewer weapons being able to be carried (possibly like 3 at the most) on Jack and maybe a slightly longer transfer time in between plasmid changes to add to the realism of the game. I love the fact that the weapons and plasmids can be upgraded; every upgrade is very noticeable, which is sweet.
Characters: Well established and convincing. Andrew Ryan and Fontaine are great villians and you really learn to hate them. Tennenbaum is the sad voice of past mistakes and you can really feel for her in that she is trying to make up for her sins (the little sisters of course). And holy sh!t Sander Cohen is amazingly funny and intense.
Enemies: The splicers are all very frightening and definitely get tougher as the game progresses to keep it tough. The security bots are a great helping hand if you hack them... or not, you can just blow them away.
Tonics and the Research Camera: It took me about my 3rd play through to realize just how important the research in this game is. It is such a big help (especially with the automatic successful hacks on the turrents and flying bots). The tonics are always cool (my personal favorites are 'Natural Camouflage' and 'Wrench Jockey / Lurker').
Conclusion: The best game I have ever played (I prefer it over Bioshock 2 just by a little) in my 16,000 points of gaming history. I have beaten it 6 times and will likely play it again because I enjoy the intensity and fun of the game so much.
Couldn't be better.
"A man chooses, a slave obeys."