Video games and science fiction go hand in hand, since a lot of games tend to wander into the science fiction world. There are numerous games that have a basis of science fiction, but one game I want to talk about personally is Fallout 3. I believe this game does the best job at exploring a "what if" situation, and also relating heavily to science fiction.
Fallout 3 takes place in post apocalyptic Washington D.C. which is just cool by itself. The whole game takes place as if the cold war actually happened, with Russia and the U.S. dropping nukes on each other. This game did an excellent job of making the significant landmarks of Washington D.C. look irradiated and destroyed. Very cool, makes the game fun just wandering around not doing anything but site seeing. (I used to have a lot of time on my hands)
It is easy to tell the technology in the game took a different route than real life did, and sort of stopped progressing right as the bombs dropped. This is difficult to explain, but everything in the game is basically tech savvy 1950's equipment. There are laser rifles, plasma rifles, etc. but they really look like they were made in the 1950's. Fallout 3 did an awesome job of this. In this picture is a car that definitely looks like it from the 1950's. I don't know much about cars from the 50's but it looks something like a thunderbird.
The story line is also amazing, probably the reason it got game of the year. The main story line is finding your father who left the vault you were in, making you an orphan. Your mother died giving birth to your character so you've only ever had your father, and when he leaves the game begins. You get bits and pieces of his where abouts, but its up to you to really find him. That is the beauty of the game. You don't even have to follow through with the main quest if you don't want to. You could easily play for many days without even regarding the main story line... The game is that huge.
There are a number of expansions for this game too, to keep the material up to date and interesting. There have been 4 expansions, all of which probably take about 6 hours to beat. That is an extra day of play time! The expansion "Point Lookout" includes a part where you have to join a religious cult. Joining requires picking berries from this enormous tree in a swamp, and when you do so, you are sprayed with some type of drug unexpectedly. Your character than proceeds to hallucinate for about 5 minutes, and the designers did an awesome job of this. It related heavily to the story line aside from just being highly entertaining. A link to the trip can be found here. http://www.youtube.com/watch?v=o061K4Ecpp0
Overall, Fallout 3 is the pinnacle of human achievement. There are MANY reasons this game got game of the year! Play it!