Heretic II fixes for problems on modern systems
This guide is based around installing and running an original CD version of Heretic II to a post-XP Windows machine. Any rig still running Windows XP should have minimal problems running the game without additional tweaks, aside perhaps from the OpenGL fix. Some of the tips might be helpful for WINE setups as well but as usual with WINE, your mileage may vary.
Part 1 - Installing
The autorun file on the CD will throw an error on 64-bit Windows, as it is a 16-bit program and 16-bit software support has been dropped from more recent Windows versions. However, the actual Heretic II installer is 32-bit and should run fine for as long as 32-bit programs stay supported. Explore the CD, go into the "setup" folder and run SETUP.EXE to install.
Part 2 - Hardware Rendering
It is generally possible to run the game with software rendering without issue, but you probably want one of the hardware accelerated modes for the full experience. The option you want for this in the settings is OpenGL32, don't bother with any of the others as they're geared towards specific, obsolete hardware. Heretic II is based on Quake II and has the same ref_gl.dll error that may crop up. However, bear in mind that not every system will be affected by this problem so It's worth trying the OpenGL32 renderer before applying any patches to see if it is necessary. If you do have an issue, it is fixed in the same way as the Quake II bug, by patching the offending line in the .dll. A prepatched version is included with the unofficial v1.07 patch set.
Part 3 - CD Audio
Playback for the CD music tracks is the third area that may be problematic. If the CD tracks don't play, or play once but don't loop after reaching the end of the track, you'll want to apply an "_inmm" patch in order to play the OST off of your hard drive. This is a generic patch system that works with many games.
Important! When following these instructions note that the file to patch in the patching step is not Heretic2.exe, but rather quake2.dll.
Now you'll be able to enjoy the OST in all its Schilderian goodness, without it falling to silence.
Note that this is purely an audio fix and does not "no-CD crack" the game. It will still ask for the CD to be in the drive when you play, even if you're not playing the OST directly from it.
If you have difficulty with crashing problems after the intro cinematic when attempting to start a new game, it is possible to avoid them by bypassing the intro using console commands. Rather than starting a new game from the main menu, open the console and set your skill level with "skill <#>" and then jump to the first level with "map ssdocks".
The skill variable values are 0 for "Adventure", 1 for "Action" and 2 for "Armageddon" with 1 being the default if you don't bother to set it. It's supposedly also possible to set it to 3 for a secret "hard plus"/"nightmare" skill (increased enemy aggression, probably, I didn't observe it to be a major effect in a quick test).
If you know a better solution to the intro crash, let me know.