Half Life 2... What is there to say about this game that hasn't already been said? This is one of the best games of all time, and I believe that you cannot call yourself a true gamer until you have played it. Half Life 2 has all the elements of a stellar video game: action, suspense, character development, challenge, puzzle, back story, gameplay mechanics, and extreme innovation.
The feel of this game is like no other; you assume the role of a theoretical physicist in a dystopian future where an alien race has enslaved most of humanity. Playing this game you will literally feel the triumph and the loss of the human race. You will experience the horrors and the adventures of the dystopia. And above all, you will fight for freedom in this near-perfect video game.
Garry's Mod is by far the best sandbox game available. This game combines amazing features such as ragdoll face and finger posing into one awesome sandbox that you will never get bored in. With it's advanced properties and mechanics that obey the real life laws of physics, this game stays true to the realism of the scale of the real life... Except for, that is, the ludacris amount of hilarity that ensures once you break that scale by, say, creating a rocket out of a watermelon.
This game also provides 100% user submitted models, weapons, and maps that add to the game's infinite possibilities. With thousands of models to choose from, and thousands of tools to use, and thousands of maps to play on, and thousands of ways to execute various tasks; you will find that one does not simply become bored while playing Gmod.
Bioshock is an amazing game that combines action, horror, adventure, shooter, and puzzle. This game provides a great deal of difficulty and has a wide range of weapons and power ups you can choose to aid you in your trek through the city of Rapture, destroyed by anarchy. The power-ups and weapons in this game are absolutely brilliant, and the story of this game is phenomenal.
Set in 1960, this game delivers a feel similar to that of Fallout. With the extreme detail, great voice acting and stellar character development, you feel as you are really assuming the role of the protagnist in that decade. Overall a brilliant game that will have you excited to progress through levels until the ending.