What can be said about Myst that hasn't already been said. Myst has been called both the savior and murderer of adventure games, and the debate about its place in the canon still rages. What is clear is that Myst changed all expectations afterword with its amazing visuals and puzzles. I can still remember going out and buying our first sound card so that we could hear this game properly. This game affected our family quite a bit. Myst and its sequel Riven is what inspired my brother to become a game designer (he now works for a major firm) and it inspired countless other imitations, homages and rip-offs.
If you haven't played Myst (what the hell?) it places you the character in a bizarre island, whose central feature, a burnt library features two books, each containing a broken message from people trapped inside them. You must search through the island for various linking books that take you to other words. All the while you'll be solving puzzles, and exploring. There are no enemies in Myst, just ambiance, allowing you to solve these puzzles at your leisure, just beware the twist at the end.
Myst has often been accused of having a less than stellar ending. And while that was certainly true when you had to wait years and years for the sequel, in this case, GOG will likely have Riven out in a few months. So download Myst for old times sake, it never disappoints.