steamapps.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication7
{
    internal class Program
    {
        private static void Main(string[] args)
        {
            var sw = new Stopwatch();
            sw.Start();
            foreach (var p in GetSteamAppsFolders())
                Console.WriteLine(p);
            
            sw.Stop();
            Console.WriteLine($"Done. Took {sw.Elapsed}");
            Console.ReadLine();
        }

        private static IEnumerable<string> GetSteamAppsFolders()
        {
            return DriveInfo.GetDrives()
                .Where(d => d.DriveType == DriveType.Fixed)
                .SelectMany(d => GetSteamAppsFolders(d.RootDirectory.FullName, 0));

        }

        private static string[] IgnoredFolders =
        {
            @"C:\Users",
            @"C:\Windows",
            @"C:\UserData",
        };

        private static IEnumerable<string> GetSteamAppsFolders(string path, int depth)
        {
            string[] directories;
            try
            {
                directories = Directory.GetDirectories(path);
            }
            catch
            {
                yield break;
            }

            //Console.WriteLine(path);
            foreach (var directory in directories.Except(IgnoredFolders))
            {
                if (Path.GetFileName(directory) == "SteamApps")
                    yield return directory;

                if(depth < 4)
                    foreach (var r in GetSteamAppsFolders(directory, depth + 1))
                        yield return r;
            }

        }
    }
}