Ok on the opening GOG.com screen it tells me the game is 80 percent off and costs $5.99 but on the store page for the game it says it is only ten percent off and costs $26.99. What's going on?

If you have the original Observer, it should be -80%. If you don't, it will be -10%. If you bought the original game, try adding it to your basket and going to the checkout and it should show you the -80% discount.