The differences between the original and the version here are very minor. There were some animation and AI issues that were fixed. For example there were some enemies that appeared in groups but only attacked you one at a time. There was also a change made to the pit level, before you could open the door to Pope Joes area you had to find the valve handle. In the new version that handle is already in place, which saves you a few minutes of needless fetching. The big thing that I wish GOG would make available if the developer commentary. In the original version of Butcher Bay you would unlock the commentary option after you finished the game. This would put floating icons throughout the game that, when activated you hear the commentary. Some of the tracks go on for over 10 minutes, but they automatically pause if you walk too far away. If you have played with the commentary in Valve games like Half-Life 2 or Portal it is pretty much the same, except that Butcher Bay did it years before. The commentary was removed from the game when it was re-released with Dark Athena and was made into DLC exclusive to those who bought the game from select retailers. Atari later offered it as part of a patch on their website and if you look around you can still find it. Since the commentary was intended to go with the original version some of it no longer applies, but it is still well worth getting if you are a fan of this game.