There's a name that you see quite a bit during the beginning credits of many period dramas, and it's Andrew Davies, the screenplay writer. He has written the screenplays for many period dramas: Pride and Prejudice (1995), Middlemarch (1994), Emma (1997), The Way We Live Now (2001), He Knew He Was Right (2004), Little Dorrit (2008), Sense and Sensibility (2008), Wives and Daughters (1999)... The list is huge!
My opinion of him is a little mixed, though. So here is my opinion on his screenplays, both the good and the not-so-good.
1. He stays pretty close to the original novel
When I first read Pride and Prejudice, I noticed how the 1995 miniseries was very close to the book. Really, I can only remember a couple of differences between the two. And one of the positive points about 2008 Sense and Sensibility was that, plotwise, it stayed fairly close to the book (as much as I love the 1995 Sense and Sensibility - which is still my favorite Sense and Sensibility adaptation - the plot wasn't as close to the book as it could have been). From what I've both read and seen an adaptation of, Andrew Davies keeps fairly close to the story line. Sure, some things are different (which is hard to avoid), but overall, he stays close to the book.
2. He keeps most of the language from the original novel
For a lot of screenplay writers, language can be modernized which can be a little annoying. Andrew Davies has a way of keeping the original language and at the same time make it lively (or maybe that's more of the actors that do it, but surely the script has something to do with it). He doesn't really modernize the language in his screenplays (at least, nothing that I've noticed) which I like since it is more believable for the time period.
With any story, there are going to be little gaps in the books. With Jane Austen, for example, sometimes there isn't dialogue in a scene, but instead the scene is described (a number of the proposal scenes, for instance, as described). What Andrew Davies does well is that he fills in those little gaps where there is not dialogue in the book with his own dialogue and makes it sound like it came from the original author. It is a talent that is very useful for writing screenplays.
1. He writes great screenplays...when he has enough time.Many of Andrew Davies's greatest screenplays are for miniseries: in other words, it takes 4+ hours to tell a story. When you have four or more hours of time for a period drama, you really get a good sense of the characters and the story. By the end of the miniseries, you really understand nearly the whole story and really understand the characters. However, when Andrew Davies only gets two, maybe two and a half, hours for a screenplay, something goes awry. The screenplay that comes to my mind is the 2007 Northanger Abbey. Northanger Abbey 2007 had the makings of a great period drama: great cast, great costuming, great scenery. But the screenplay was lacking; many things were left out in order for additional scenes (more on that). Two hours, in my opinion, wasn't enough to tell Northanger Abbey without the additional scenes, let alone with all the additional scenes.
2. Less is more
3. Skipping Scenes (or Worrying about Skipping Scenes) is Not FunThis kind of expands off of two, but it's kind of on it's own too. For the most part in classic literature, nothing gets graphic or is shown. If any scandal is mentioned at all, it's mentioned very discreetly. Therefore, it is unnecessary to add those scenes considering that you could completely skip those scenes and not miss anything in the plot. Andrew Davies (it seems recently) has been adding these unnecessary scenes. For example, in the Sense and Sensibility, you don't hear about any scandal until the second half of the book, and even then it's very brief; in the 2008 version, the scandal that was so briefly mentioned was shown in the very first scene. Or how in Northanger Abbey 2007, Catherine's dreams were a bit mature for her, and considering Catherine's innocent nature, this was not only inaccurate, but also unnecessary. Or in Little Dorrit there was the one scene that was a completely different scene in the book. These scenes take what would otherwise be great period dramas and make them a little difficult to watch. Sure, they can be easy to skip if you know what to look for, but it's not fun waiting to skip scenes; it's much preferred to simply watch a period drama all the way through. He didn't always add in these kinds of scenes -- Pride and Prejudice, Wives and Daughters, and Emma got along well without them. This seems to be more of a recent trend. You don't need those scenes to make a great period drama.
That would summarize my opinion on Andrew Davies's screenplays. Overall, the man is talented in writing screenplays, but when he does one or more of the three things that aren't so good, the screenplays aren't as good. We can hope that his future period dramas don't have some of the problems that some of his screenplays have had...