what is the difference between full game and the add-on???
is it only the size.??204MB and 500 byte..

If you've played the previous GOTM's, you have most of the files already installed that you need. In that case, the add-on download would be the proper one, as it only contains the new files that are needed.

The full download contains all the files that are needed, and is for those who haven't installed the other GOTM file packages for games 16, 17, 18, and/or 19.