Portal: Its a short game, but I saw that coming. However, I cant remember the last time I had so much fun playing a game. The spooky atmosphere provided by the Aperture Science psycho computer GLaD-OS, and the use of nothing but the Portal Device to solve some insane puzzles makes for an amazing experience. Also, Jonathon Colton wrote a song for the end credits sang by GLaD-OS herself called "Still Alive", which of all the reviews I have ready to day everyone enjoyed greatly. Its a hilarious song with many inside jokes from the game. I even put it on my iPod I loved it so much.
HL2 Episode 2: Picked up right where Episode 1 left off, but instead of the repetitiveness of Episode 1, they improved on absolutely everything everyone bitched about, and contains some of the most emotionally charged sequences in a Half Life game to date. You also find out the relationship between Aperture Science (Portal) and Black Mesa (Half Life) in Episode 2. They improved the AI of your Enemies and Allies alike, and also added a new enemy, called a "hunter", which is like a mini-strider. These little buggers of ruthless. If you find cover, they find a way to get around it. If you hide in a house, they will break down doors and windows to find you. Like Episode 1, the game ended with an insane cliffhanger that will definitely get me to play Episode 3.
Team Fortress 2: If you enjoyed the original Team Fortress for Quake, you will really enjoy Team Fortress 2. Unlike how Team Fortress Classic changed many of Team Fortress' dynamics, this game is much more faithful to the original, and provides hours of enjoyment. The rock-paper-scissors class system ensures that no class cant be stopped by another.