ZDoom is a version of Doom able to play the IWAD files of any Doom game, but with much improved grahpics, physics, options, and blood effects, ZDoom also carries the ability to use FREE LOOK. You may use ZDoom to play Behold the Darkness, however, there is a plus side and a minus side. The plus side is that you can use free look while playing Behold the Darkness, and the secrets work perfectly and don't always come out as 0% at the end of a level. But the minus side is, it may become pretty laggy at some points lasting for only a little bit, and you may not choose levels when you start up the game.
While using the regular old DOOM95 version of Doom II, it is very classic, but the secrets don't work, and always come out as 0%.
Take your pick, ZDoom, or DOOM95. Of course, you may play both of them in moderation, I am just presenting the compatability this mod has with ZDoom.
