public static void DownloadDirectoryFromFtp(string ftpUrl, string localFolderPath, string username, string password)
{
    Queue<Tuple<string, string>> directoriesQueue = new Queue<Tuple<string, string>>();
    directoriesQueue.Enqueue(new Tuple<string, string>(ftpUrl, localFolderPath));

    while (directoriesQueue.Count > 0)
    {
        var current = directoriesQueue.Dequeue();
        string currentFtpUrl = current.Item1;
        string currentLocalPath = current.Item2;

        FtpWebRequest request = (FtpWebRequest)WebRequest.Create(currentFtpUrl);
        request.Method = WebRequestMethods.Ftp.ListDirectoryDetails;
        request.Credentials = new NetworkCredential(username, password);

        using (FtpWebResponse response = (FtpWebResponse)request.GetResponse())
        using (StreamReader reader = new StreamReader(response.GetResponseStream()))
        {
            string line = reader.ReadLine();
            while (!string.IsNullOrEmpty(line))
            {
                string name = GetFileNameFromFtpLine(line);
                string permissions = GetPermissionsFromFtpLine(line);

                if (permissions.StartsWith("d"))
                {
                    string subfolderFtpUrl = currentFtpUrl + "/" + name;
                    string subfolderLocalPath = Path.Combine(currentLocalPath, name);

                    if (!Directory.Exists(subfolderLocalPath))
                    {
                        Directory.CreateDirectory(subfolderLocalPath);
                    }

                    directoriesQueue.Enqueue(new Tuple<string, string>(subfolderFtpUrl, subfolderLocalPath));
                }
                else
                {
                    string fileUrl = currentFtpUrl + "/" + name;
                    string localFilePath = Path.Combine(currentLocalPath, name);
                    DownloadFileFromFtp(fileUrl, localFilePath, username, password);
                }

                line = reader.ReadLine();
            }
        }
    }
}

public static void DownloadFileFromFtp(string fileUrl, string localFilePath, string username, string password)
{
    FtpWebRequest request = (FtpWebRequest)WebRequest.Create(fileUrl);
    request.Method = WebRequestMethods.Ftp.DownloadFile;
    request.Credentials = new NetworkCredential(username, password);

    using (FtpWebResponse response = (FtpWebResponse)request.GetResponse())
    using (Stream responseStream = response.GetResponseStream())
    using (FileStream fileStream = new FileStream(localFilePath, FileMode.Create))
    {
        responseStream.CopyTo(fileStream);
    }
}

private static string GetFileNameFromFtpLine(string ftpLine)
{
    string[] tokens = ftpLine.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
    return tokens[tokens.Length - 1];
}

private static string GetPermissionsFromFtpLine(string ftpLine)
{
    string[] tokens = ftpLine.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
    return tokens[0];
}