Portal 2's story had its highs and lows. Although it might not have been very rewarding in the first place, sometimes even repetitious and boring, the ending of Portal 2 reveals the game's true ingenuity.
This article examines what makes Portal 2's experience so different and why Valve is the only developer that creates stories perfectly fitting the medium of video games.
Note: This article contains SPOILERS, obviously. Also, though the site has a .de ending, the article is completely written in ENGLISH.