Como posso fazer isso na interface do usuário c # moderna?

var url = "http://ajax.googleapis.com/ajax/services/feed/load?q=http%3A%2F%2Fwww.digg.com%2Frss%2Findex.xml&v=1.0";
var wc = new WebClient();
var rawFeedData = wc.DownloadString(url);

//You can use System.Web.Script.Serialization if you don't want to use Json.NET
JavaScriptSerializer ser = new JavaScriptSerializer();
FeedApiResult foo = ser.Deserialize<FeedApiResult>(rawFeedData);

//Json.NET also return you the same strong typed object     
var apiResult = JsonConvert.DeserializeObject<FeedApiResult>(rawFeedData);

Isso me dá erro um erro no WebClient eSystem.Web.Script.Serialization