Myst is the first game I played that felt a little more grown up. Before Myst I was mostly playing simple arcade style games which fun never really challenged my mind at all. At the time my computer could barely handle the game and crashed a lot on me which is hilarious looking at the system requirements now.
I give Myst a 5 out of 5 because it was a game that I truly enjoyed on every level. The visuals are a little dated now but at the time I thought it was one of the best looking things I have ever played. As you go around from age to age the surroundings really set the mood. A place or two was even eerie enough to scare me into not playing alone (I was a lot younger then mind you). The gameplay itself was very simple. You just walk around and move your mouse over things to manipulate them. Puzzles required some thought and a little research by having to read a journal about that age you were going into. The replay value is a little low because once you understand the puzzles it doesn't take much to remember them. I am sure I can now beat the whole game in under an hour even though it took me much much longer the first time I played it.
Oh, one other things about the Myst series I have always loved and I hope other people are able to have similar experiences is to play with someone else. My siblings were playing the game too and we each had our own save file but we would watch each other play. Then we would bounce ideas off of each other to figure things out.
Myst opened up a whole genre of gaming too me and I only wish that most of the Myst clones out there were able to live up to the same standards.