I have neither read the book on which the movie is based, nor the letters between Vita and Violet. If I came to this movie with any expectations whatsoever, it was maybe that the Bloomsbury group (including among others Virginia Woolf, and which the Nicolsons were part of) would be depicted. It wasn't, which however wasn't a problem for me. What I am wondering about is how the people behind this movie managed to make it, in my opinion, so very uninteresting and repetitive and most of the characters flat, in spite of great material and some very good actors. The script is simply not good enough. I agree with the criticism of my Finnish neighbor - too many pointless sex scenes (but only between the women, while there is nothing explicit whatsoever concerning Harold's numerous love affairs), too many pointless scenes in general, too little information about the background of characters. It seems odd considering the quality of the production - on the surface it seems a really ambitious piece of work, but the script holds of course the most weight and that is where this movie fails.
Vita's relationship with Harold struck me as unconvincing, although both of them act really well, especially her. The way they kept declaring their unconditional love for each other in a rather sappy manner I thought, well, simply unconvincing. It makes a lot more sense that it should have happened through letters, as tmmvds points out I would also have liked to know where the nicknames came from - the Russian ones* as well as Mar - why ever is someone called Vita given the nickname Mar? It might be small stuff, but it matters in contributing to the bigger picture.
*I watched the movie with English subtitles on, and where it should apparently have said Mitya, it said instead Medea. That might explain my frustration with the nicknames to some extent - I could not understand why Vita's should be Greek while Violet's was Russian!