How to install and play on Ubuntu, 14.04 onwards

Download the linux version of Baldur's Gate Enhanced ,
Baldur's Gate II Enhanced or Icewind Dale Enhanced

Then you need these to make it work. Open a terminal (ctrl+alt+t) and copy/paste the following:
sudo apt-get install libc6:i386 libasound2:i386 libasound2-data:i386 libasound2-plugins:i386 libgl1-mesa-glx:i386
type password in, and press enter and enter or y to install.

The .sh files from GOG.com are better than the old files as it even has a shortcut on the desktop if you want it to. As far as I know, if you own the GOG.com game you can download it as many times as you need to for free. It might be useful to log into GOG.com occasionally to see if there are any patches

In your Files maximise the window and under Edit select Preferences. In the behaviour tab, under the Executable files, select Ask each time and close the window. This only needs doing once. Once you've done that you simply right-click on the .sh file and select properties. Under the permissions tab tick Allow executing files as program and close the window. You have to do this on every file. Now you should be able to install it by left-clicking and running the file. You can then play by clicking on the shortcut on your desktop if you chose to have one. You can resize the shortcut to make the picture smaller by right-clicking resize icon.

You'll find the saved games are hiding. Inside Home press ctrl+h and then you will find the saved games in
.local/share/Baldur's Gate (or Baldur's Gate II) - Enhanced Edition/save
I'm not entirely sure but the saved games appear to be compatible with Ubuntu, Windows and Android so you shouldn't have to start again just because you change OS. Android saved game location is: Internal storage/android/data/com.beamdog.baldursgateenhanced or Internal storage/android/data/com.beamdog.baldursgateIIenhancededition. I hope you have lots of fun adventuring 'round the Sword Coast.

If you have tar.gz files

GOG.com now has different files but I'm leaving the following instructions as they should work for any tar.gz files if you type the correct name of folder and .sh file.

Extract the tar.gz file and put the entire folder where you want to. I recommend you rename the folders to make it easier. If you have put them in Documents, then to run you type the following in a terminal (ctrl+alt+t)
~/Documents/nameoffolder/start.sh or if you put them on the desktop it's ~/Desktop/nameoffolder/start.sh
Don't put sudo at the beginning otherwise only root will have full access to it.