It's not terribly often I come across writing I consider to great because of what I feel is the confluence of events required to reach this level of... great.
Well written, you most definitely have to have that. Beyond that, the subject has got to either hold a certain gravitas of import or at the very least, be interesting (I write in this blog post about an example from Charles Pierce meeting this dual criteria).
Additionally, you might have some context of solid writing thrown in... typically in the form of work by someone you already like, but as this post will detail, there's another type of good writing context that can be in evidence.
Point of all this is to say that it takes a lot to make a piece of writing great and the follow on point is "The storyteller and the stallion" by Roger Ebert is great writing. Written on his Chicago Sun-Time blog, the work is about Ebert's college friend Bill Nack... including his life in writing (25 years of which spent at Sports Illustrated) and his authoring of the book Secretariat, since made into a movie.
From a writing perspective, it's really well done work by someone I'm tremendously impressed with as an author in Ebert. Additionally, I find it incredibly cool that one of my favorite current- day writers, Joe Posnanski, would link to the story on his twitter account and refer to Ebert and Nack as two of his favorite writers (very similar to the way Posnanski mentioned another one of my favs, Chris Jones, in an SI blog piece a few weeks ago).
From a subject perspective, I enjoyed this Ebert piece not because it's got content about horse racing, but because it weaves a tale of both the relationship betwixt Ebert and Nack and writing itself. Now, the phrase writing itself may seem a bit melodramatic to use, but what got me was how the piece is someone with both a proven love for words and the process of writing them detailing a friend and his love for words and the process of writing them.
To boil it down... that's just cool, and results in a piece of great writing.