I still have the original and am looking to buy this, but the major thing that always caused me an issue was the "ethereal potion bug" mentioned here: http://www.ataricommunity.com/forums/showthread.php?t=172354. Is this something that has been fixed in gog version?

The page http://www.ataricommunity.com/forums/showthread.php?t=172354 doesn't load... (at least for me).
It seems there's a problem with the host server www.ataricommunity.com.

Can you describe the problem?

How odd. Essentially, there is a monk in the game that you find as part of a monastery . He gives you an ethereal potion and you drink it so you can get Reubens key to open up the windmill (i think it was a windmill). An error could occur when you drank the potion and you could not progress unless you were lucky enough to get past the bug. the following is on the page I linked to but it would never work for me:

When the monk gives me the ethereal potion and my character drinks it, the game crash.
Solution 1: Make sure the character drinking the ethereal potion quaffs a potion of enchanted armour PRIOR to speaking with the monk and getting the ethereal potion.
Solution 2: Remove ALL magic orbs and wield normal weapons/armours instead.

I played it all day, and now im stuck becuse i cant get past the monk. Ive tried everything. Removing orbs
use normal weapons,
not wearing any weapon.
Used the potion before talking to the monk.
Used the potion on everyone in my party and removing all weapons.
Tried chaning party.

Im starting to loose hope... Ive been searching for a savefile to get me past that point but every savefile i found sofar has been cheated. Why would you cheat in a game like this anyway.... .:((((

I feel your pain, as I had the same thing when i first played. The only way I ever got past it was just luck... the one time it didn't crash, I was able to get the key and save. Looks like it's not solved then.