A method that removes all tags from html except those that are on the acceptableTags array, and raw text nodes.

HtmlUtilites.cs

using System.Collections.Generic;
using System.Linq;
using HtmlAgilityPack;

namespace Amberizer
{
    public class HtmlUtilites
    {
        public string RemoveUnwantedTags(string data, string[] acceptableTags)
        {
            var document = new HtmlDocument();
            document.LoadHtml(data);


            var nodes = new Queue<HtmlNode>(document.DocumentNode.SelectNodes("./*|./text()"));
            while (nodes.Count > 0)
            {
                var node = nodes.Dequeue();
                var parentNode = node.ParentNode;

                if (!acceptableTags.Contains(node.Name) && node.Name != "#text")
                {
                    var childNodes = node.SelectNodes("./*|./text()");

                    if (childNodes != null)
                    {
                        foreach (var child in childNodes)
                        {
                            nodes.Enqueue(child);
                            parentNode.InsertBefore(child, node);
                        }
                    }

                    parentNode.RemoveChild(node);

                }
            }

            return document.DocumentNode.InnerHtml;
        }
    }
}