While Portal feels almost as if its a DLC or workshop map for Half-Life 2, it cannot be denied that the level design in this game is astonishingly good. Using a very simple mechanic - a portal here and a portal there - the test chambers get increasingly more complex and, when finished, impress you with just how ridiculous the level design is. While the story is there but not entirely developed, the foundation for what I believe to be one of the best games ever made was made.