It's not a masterpiece, but...
Serena is a quite passable period film. Perhaps it's because I'm a huge fan of Suzanne Bier but I don't understand the vicious criticism against Serena. Given Serena's reputation, I kept waiting for the film to take the plunge into nonsensical absurdity and it never really did.
It seems like critics especially have chosen to pile on this film for fairly arbitrary reasons (18% on Rotten Tomatoes, really?). IMO, Serena is fairly comparable to the recent period dramas I've watched like Far From The Madding Crowd and the Imitation Game - both of which received warm receptions.
Listen, this film is not a masterpiece, and if you're new to Bier you should watch basically anything else. But period dramas are by their very nature slow paced, fairly stylistically conservative, and steeped in melodrama. So is Serena.