The original Portal had the element of surprise. Its style of first-person physics-based puzzle gameplay was unique. GLaDOS, the murderous robotic villain, was new and vibrant and evil in the most charming way. Cake jokes and songs about surviving dismemberment were still hilarious. It was short, succinct and essential. Creating a sequel without playing all the same notes and making it feel like Portal: The Longer Version is a tough task. For Valve, it's apparently no problem...