[Sage]

Squarejaw is correct: Myst tends to polarize people's opinions.
In it's day, the original Myst was the best-selling computer game of all time, and it's high sales figures ushered in what some consider to be the "Golden Age" of adventure games.
The Myst series does require a slightly higher than average level of mechanical aptitude, but nothing extraordinary.
Antionetta is also correct: Constantly swapping CDs in Riven is a huge pain, so the recently-released 10th Anniversary DVD Edition of the first three games is well worth the price if you're DVD-ROM equipped, plus it has a much-improved version of the original Myst.
If your current system is not DVD-capable, the first three games in the series are widely available used for very little money. Riven and Myst III-Exile are multi-platform, but the original came in separate versions for Mac, DOS, Windows, and Panasonic 3DO formats, so make sure the copy you buy is the one you need.

ScottMate