Half-Life is the best. You won't regret buying it. It's like a 100 games in one : There are tousand mods for this game (they are not all very good but many are so good like Counter-Strike, Day of Defeat, The Specialists, Naural Selection, etc...) However the graphics are not very very good because the game is 5-6 years old, but it still stay on the road ! (See Day Of Defeat graphic, it is so beautiful for an old game).