Portal

Amazing puzzle game that honestly instilled in me a love of the genre. It's incredibly short, with one playthrough taking around two hours, but it kept me hooked the entire time. The puzzles themselves are pretty tricky at points, but nothing a little determination won't solve. Additionally, there are usually multiple ways to complete courses which gives the player some freedom. Usually, games just demand you complete the puzzles as the developers intended, so this is a breath of fresh air. Achievements are pretty straight forward with the only difficult one requiring you to achieve all the gold medals for six levels. Medals are given out for completing each level with the least amount of portals placed, the least amount of steps taken, and the least amount of time accrued. These are a pain to get, but I honestly enjoyed learning the different speed running methods used to make this achievement easier. Overall, this is an underrated classic that is overshadowed by it's much bigger brother, Portal 2, and everyone must pick it up. Valve only makes PEAK.