string tempStr = File.ReadAllText(@"C:\Documents and Settings\Administrator\桌面\Test.txt", Encoding.GetEncoding("utf-8"));//读取txt
                string pattern_1 = @"(?i)<div[^>]*?class=(['""]?)game_info1\1[^>]*?>\s*?<p>[\s\S]*?<a[^>]*?>([^<>]+?)</a>[^:：]*?[:：](\d+)[\s\S]*?</p>";
                pattern_1 += @"\s*?<p>[^<>]+?(<a[^>]*?>(?<text>[^<>]+?)</a>\s*?)*?</p></div>";
                //tempStr = Regex.Replace(tempStr,pattern,"<tr>$0</tr>");
                foreach (Match m in Regex.Matches(tempStr, pattern_1))
                {
                    //循环输出
                    // 
                    string t1 = m.Groups[2].Value;//儿童小游戏
                    string t2 = m.Groups[3].Value;//205
                    string t3 = string.Join(",", m.Groups["text"].Captures.Cast<Capture>().Select(a => a.Value));//幼儿教育,学习类

                }

------解决方案--------------------

第二个注意你div的开始和结束地方
C# code
string tempStr = File.ReadAllText(@"C:\Documents and Settings\Administrator\桌面\Test.txt", Encoding.GetEncoding("utf-8"));//读取txt
                string pattern_2 = @"(?isx)<div[^>]*class=(['""]?)operate\1[^>]*?>((?><div[^>]*>  (?<Open>)|</div>  (?<-Open>)|(?:(?!</?div\b).)*)*(?(Open)(?!)))</div>";
                string result = Regex.Replace(Regex.Match(tempStr, pattern_2).Groups[2].Value, @"<!--[\s\S]*?-->",string.Empty);
                /*
                 * <div id="GameKey">
                    <ul><li><SPAN class=ico_c_mouseleft></SPAN>鼠标操作</li></ul><div class='clear'></div><div class="game_cz_fg"></div>
                    <div class="clear"></div>
                    </div>
                    鼠标控制移动，左键点击调下踩跷跷板，注意要踩到正确的答案哦！
                 */