Binderman: I own all the original games and sometimes I play them on my old computer with Windows XP installed. Is it worth for me to buy this pack?
If you already have the games and can play them without spending too much time configuring them, you already have what GOG offers, though not in a simple to use installer.
If to play the games you need to spend some time properly configuring them, the question is if the time you spend is worth $9.99. Same is true if you are missing any of the 6 games (QfG1 EGA, QfG1 VGA, QfG2, QfG3, QfG4 cd version, QfG5).
In all cases though, you may want to keep an eye out in case it gets a 75% or more discount, since $2.49 for a digital backup does sound like a good deal.
