I don't buy a lot of TV series on DVD (read, any). Dang, that's not true. On the back of a pleasant evening in the theater with State of Play, I bought the BBC mini-series on which it is based.
All I can say is, wow. A much better all around production. Six hours gives a lot of time to develop characters. The series is much more journalistic-procedural than the film, which is good. Excellent music. I love Kelly Macdonald's accent. Bill Nighy is amazing as usual.
Solid drama, worth your money over the film version. The film has some elements in its favor, such as the old media/new media tension, and Helen Mirren. That's not enough in the end. The original is better.