The following is how we our datasets:

public static List<DataSet>ImportDatasets()
{
  var dialog = new OpenFileDialog
  {
    Multiselect = false,
    Title = "Open Dataset File",
    Filter = "Text File|*.txt;"
  };

  using (dialog)
  {
    if (dialog.ShowDialog() != DialogResult.OK) 
    return null;

    using (var file = File.OpenText(dialog.FileName))
    {

Deserialize the data and return it:

      return JsonConvert.DeserializeObject<List<DataSet>>(file.ReadToEnd());
    }
  }
}