Great package with more HL2, a witty mind bending puzzle game, and divine multi-player for the masses.
Portal advertised itself to be a new kind of puzzle game and it does that brilliantly. It gets extra credit for dry, dark, wittiness that I found laugh out loud funny. Most fun I've had playing a game in a long time. Again short: 2-4 hours.
Team Fortress 2 is a highly refined multi-player game with game mechanics that don't grossly favor the elite players. There's an advantage to being good and being smart in this game, but it's not so exaggerated that a casual player can't function. Class variety is a blast and the style of this game is a hoot. Lots of replay value here.