I found an article online while surfing the net earlier this week and thought I would share it with you guys. It seems someone went and took the time to port doom into Half life 2 and is releasing it for Garry's Mod. It will let you put doomguy and all the stuff from doom into Half Life 2 and play it in HL2, you can also play HL2 as doomguy using all the weapons and stuff from Doom. You can also put all of the doom enemies into HL2 and fight them as Gordan Freeman.

Here is a link to the article which also includes a video of some gameplay for it. http://www.gameranx.com/updates/id/1...n-half-life-2/