The concept is very simple. There is a grid full of objects. When you click on two adjacent objects, they exchange places. If there are three or more of the same type of object in a row or column, the objects are removed, the objects above fall to fill in the gap, and new objects drop in at the top to fill in the gap.
So far, this is the same as Bejeweled, another very addictive game.
Jewel Quest, however, adds a twist. Whenever pieces are removed, the background underneath them turns gold. When all of the squares have become gold, the level is complete. You score a bonus for time remaining and a new level begins. And the levels are not simple rectangular grids. They come in a wide variety of shapes, making some levels extremely difficult to complete within the time limit.
As the levels progress, additional twists are added. Like "buried treasure" - objects that you have to match multiple times before they are removed. And objects that will penalize you if they are removed directly (but give you a large bonus if you can remove them indirectly). There are 180 different puzzles, so you won't be able to finish the game quickly.
Like many other puzzle games, Jewel Quest may be played full-screen or in a window. So you can choose to either pay attention to what the rest of the computer is doing or choose to get completely absorbed in the game.
The system requirements are very small by today's standards (Windows 98, 32M RAM, Direct X 7), so it should run on anything that is even remotely modern. It installed and ran without any problems on my gaming PC (Athlon 64/3200+, Windows XP, 512M RAM).
The only downside to this game is that nobody has (yet?) ported it to the Macintosh platform. I prefer to play games like this on my Mac so they can share a desktop with the other things I work on. But I recognize the fact that it takes a while for people to port games to the Mac, which is why I have a gaming PC in the first place.