Anna Karenina by Leo Tolstoy is the only book that is on all 4 of my Top 100 book lists and in my Top 10 book list (Here: Sybervision, Norwegian, Observer, BBC, and Zane's)
Now to state first off I thought this was one of the most well written stories I have ever read. Tolstoy just flows with descriptions that make you feel you understand everything that is going on. The characters are extremely well developed and even though they are Russian (which has a tendency to jump around with names a bit) it is still easy to follow who is who. I enjoyed several of the references to early communist culture (the book takes place about 30 years before the communist revolution) and several of the characters' personality polarities and themes that are emphasized in the book (religious vs non-religious, upper vs lower class, etc.).
Onto my main gripe with the story; it seems like two separate stories going on at the same time. The "main" one should be the one with Anna but I got the feeling that for the most part it was the story line centered around Levin (who supposedly represented Tolstoy himself). The story about Anna I felt was enjoyable and well written. It focused around her leaving her husband for another man which that relationship slowly dissolves over the length of the book as well. While the story with Levin, although in parts were very good, I felt was very political and sometimes unimportant to anything. The whole last section (after the Anna story line was wrapped up) felt out of place and forced and left me wishing the book would just end. All in all I very much enjoyed the first half of the novel but the second half seemed to drag on a bit. I am not going to recommend this on my list and personally would not consider this the greatest book ever. But being that it is on so many book lists it probably should be one that you read.