My personal favourite. 5 games in one great orange box; Half-Life 2, Half-Life 2: Episodes 1 and 2, Portal and Team Fortress 2.
They are all great games. Portal being my most loved (Weighted Companion Cube). The HUD is very similar in the Half-Lives and Portal. The HUD for Team Fortress 2 is different but the controls are the same. They are all very realistic - except for Team Fortress 2 - and have great music.
This is a must!