using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Newtonsoft.Json;
using Newtonsoft.Json.Converters;
using Newtonsoft.Json.Serialization;
using Newtonsoft.Json.Linq;

namespace cscliTest
{
    public class Font
    {
        public int size;
        public int color;
        public string name;
        public List<int> style = new List<int>();
    }
    public class Content
    {
        public string hi;
        public Font font = new Font();
    }

    public class Value
    {
        public int msg_id;
        public uint from_uin;
        public uint to_uin;
        public int msg_id2;
        public int msg_type;
        public int reply_ip;
        public int time;
        public List<Content> content = new List<Content>();
    }
    public class Result
    {
        public string poll_type;
        public Value value;
    }
    public class sss
    {
        public int retcode;
        public List<Result> result = new List<Result>();
    }

    public class Test
    {
        public int m_a;
        public int a
        {
            get;
            set;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            //测试数据
            sss a = new sss();
            a.retcode = 0;
            Result r = new Result();
            Value v = new Value();
            Content c = new Content();
            Font f = new Font();
            f.size = 10;
            f.color = 0;
            f.style = new List<int>(new int[] { 0, 0, 0 });
            f.name = "xxx";
            c.font = f;
            c.hi = "hello";

            v.msg_id = 32065;
            v.from_uin = 2246865592;
            v.to_uin = 1589188359;
            v.msg_id2 = 605408;
            v.msg_type = 9;
            v.reply_ip = 178848417;
            v.time = 1352614319;
            v.content.Add(c);
            r.value = v;
            a.result.Add(r);
            string xx = JsonConvert.SerializeObject(a);
            Console.WriteLine(xx);

            //方法一（需定义上面那些类）
            sss a2 = (sss)JsonConvert.DeserializeObject<sss>(xx);
            Console.WriteLine(a2.retcode);

            //方法二（不需定义上面那些类）
            JObject o = (JObject)JsonConvert.DeserializeObject(xx);
            JToken o2 = o["result"][0];
            JToken o3 = o2["value"];
            JToken o4 = o3["content"][0];
            JToken o5 = o4["hi"];
            Console.WriteLine(o5.ToString());

        }
    }
}

感觉content后面的两个[[格式有问题，所以我这里的和你的格式有点差别，请注意。
以前做过，今天翻了下，网上的太乱，以至于弄了挺久。