I'd say its a combination of roguelike, survival and basebuilding. Definitely not horror. Artistically it strikes me like Charles M. Schultz and Tim Burton had a baby. Edit: Wikipedia's description of it being an 'open world environment' also seems wrong to me. Open world implies a preconstructed world which you can explore freely. Don't Starve is randomly generated, which I think is very different, even if there are no plot corridors. Its like if you were to call Civilization or Torchlight open world.