As you can see, Doom runs with Dosbox in Steam. And this is not very comfortable, because you can't play in openGL mode or with HD textures for example. So now I'll tell you how to handle this. But firstly, what is Source Port?

A Source Port is a fan-made program that allows you to play Doom on systems not originally supported (like XP, Vista or 7) or with new features and improvements, including 3D platforms support, OpenGL graphics, mouse look, higher resolutions etc.

There are many Doom Source Ports. All of them support all Doom games like Ultimate Doom, Doom 2, Final Doom and Master levels.

The most popular Source Ports for Doom are:

• ZDoom / GZDoom[zdoom.org]
  
• Zandronum[zandronum.com]
  
• Doomsday[dengine.net]
  
• PrBoom+[prboom-plus.sourceforge.io]
  
• Chocolate Doom[www.chocolate-doom.org]
  
• Doomsday[dengine.net]

If you go to the Steam\SteamApps\Common\Doom 2\ directory, you can see there three .bat files, such as:

• doom2 + mouse.bat - starts Doom with mouse control
  
• doom2.bat - this starts Doom without mouse control (classic controls)
  
• testapp.bat - this one we won't modify

If you go to the Steam\SteamApps\Common\Doom 2\base directory, you can see there DosBox files, Doom2.exe, Doom2.wad etc.

There are 2 solutions to run Doom with any Source Port. Let's start.

Ok, fisrtly, you need to download any Source Port and extract it into:
Steam\SteamApps\Common\Doom 2\base

Then you must open doom2 + mouse.bat with notepad. In the file you will see this code:
.\base\dosbox -conf .\base\doom2m.conf -fullscreen -exit
exit

In doom2.bat you will see this:
.\base\dosbox -conf .\base\doom2.conf -fullscreen -exit
exit

So, then just delete all text in .bat file, which one you want to launch, paste this code (if you use Zandronum Source Port) and don't forget to save the file:
.\base\zandronum.exe

If you use Zdoom - paste this:
.\base\zdoom.exe

Or this one, if you use gzDoom:
.\base\gzdoom.exe

That's all. Now you can launch Doom 2 with Zandronum or any other Source Port and enjoy the game with comfortable controls and OpenGL graphics.

Also, you can do another thing - after downloading Source Port, extract it into:
Steam\SteamApps\Common\Doom2\base

Steam uses Dosbox.exe to run Doom, so just delete it and then rename zandronum.exe, for example, to dosbox.exe. That's all.

Enjoy the game:)

Find Doom 2 in your Steam library, right click on it and open properties, after that add to launch options such type of command (pay attention that you have to write there correct path to source port exe file):
"D:\Steam\steamapps\common\Doom 2\base\gzdoom.exe" %command%

Sadly, you can enable steam overlay to take screenshots only in Ultimate Doom. But anyway, using, for example, Zandronum source port, you can play any .wad starting Ultimate Doom (Doom 2, TNT, Plutonia etc.).

To enable Steam overlay you need to use mine Solution №2 (only second, because the first one doesn't work with Ultimate Doom), then open ultimatem.conf file and find there these parameters:

fullresolution=
output=
machine=
aspect=

You need to set them this way:

fullresolution=desktop
output=openglnb
machine=svga_s3
aspect=true

That's all. Don't forget to save the file :)

There are cheats that you can use in all Doom games:

IDDQD - god mode
IDFA - gives you all weapons
IDKFA - gives you all weapons and keys
IDCHOPPERS - gives chainsaw
IDMYPOS - player coordinates
IDDT - opens level map
IDBEHOLDA - area map
IDBEHOLDV - temporary invulnerbility
IDBEHOLDI - temporary invisibility
IDBEHOLDL - makes level brighter
IDBEHOLDS - rage mode
IDBEHOLDR - radiation ptotection
IDMUS## - changes level music on ##
IDCLEV## - changes level on ##
IDCLIP - allows to move through walls

If you are looking for modern textures, you can download Hi-Res textures pack here[dhtp.hiriwa.com]. There you can find textures for this Source Ports:

• Doomsday
  
• GZDoom (this one can be used with Zandronum)
  
• Risen3D
  
• ZDoom

Tired of sprites? I highly reccomend to install voxels pack.

Also, if you like heavy music, you can dowload this[dfiles.ru] WADs with metal-style original Doom and Doom 2 soundtrack.