It can be hard to articulate why a design is good, or why it just works. A great design like this just is. All of the things that make this site successful are so small, so subtle as to go almost unnoticed. To start with, the type is perfectly chosen and set. I think this is as good of an advertisement for Typekit and FontFont fonts that I’ve seen. The flawlessness, even at small sizes, of FF Dagny is just astounding. Brian could have easily used Helvetica and called it a day, but it really wouldn’t have the beauty that this does. He also could have just put a drop shadow behind the main area, but instead used a subtle pattern on either side, achieving the same separation and depth that drop shadows can provide, but going in a different enough direction to be original.
The comments count line is clever, e.g. “You will be the 24th comment”. I do feel like the link in that line should go to the comment form, not the top of the comments, but that’s minor. I could keep going, but the theme of this design is about coming up with fresh, inventive and subtle tweaks to familiar elements we’ve seen on blogs for years. I expect this to be a site that will be frequently mimicked in the near future. It’s a remarkable success.