I won't say much as others have already commented on what makes this game great. I will just say that there are still some bugs and issues that cause the game to hang. In addition there are some quality of life things from Serpent Isle that aren't implemented in Black Gate. If you've already bought and paid for the game then you'd do well to look for Exult, which patches up Black Gate a fair deal (improvements include a hotkey for the spellbook, a hotkey for 'feed', I believe a hotkey for using every key you have, etc.) Don't mean to cast aspersions on GoG. This is still an excellent game and a release that surpasses the original.
