A masterclass on building a whole experience instead of just a game, brought to you by the masters at valve. This game is a compact, funny, satisfying, well thought out puzzle experience. The research and thought that went into creating this game, calculated millimetrically, in order to provide a consistently good experience astounds me to this day and is the industry standard for quality. A good tutorial is one that teaches you to "think with portals" and pioneering those concepts is a testament to how amazing the guys at valve are at making games.