aleeque: 1) The GOG version ignores external color temperature settings made by programs such as Flux etc and runs the game in original OS color temp and gamma. Regular D1 version cannot do this. This is pretty important to me and, no doubt, many other people who use Flux.

2) The GOG version does not require the ipx wrapper, the ddraw wrapper nor the rainbow color bug fix. It also doesn't need the CD to run.

3) It looks a bit nicer with 16x antialiasing.

Yes, you can play regular 1.09 Diablo 1 without Hellfire. Also, the GOG version is compatible with Ulmo's stash mod (just put the files in /dx/ subfolder instead of root game folder and run loader.exe)