A devlopers take on Portal's devlopment

I've always enjoyed the articles I find on Gamasutra but this one was particularly enjoyable because Noah Falstein took one of my favorite games from last year broke it down and explained (not in minute detail) why the different elements of the game made it so much fun to play. Of course one of the great things about articles on Gamasutra is that the comments are always intelligent because they're made by people in the industry.