Take a classic puzzle game (think Bejeweled), add RPG elements and a plot progression where all battles are carried out through that puzzle sequence where both players alternate while sharing the board, and you've got the general idea of what Puzzle Quest is.
Puzzle Quest is a silly wrapper around the puzzle game which ends up strangely compelling - you get special abilities your character can use which use "mana" depending on which colored jewels you combine. You collect experience and money by matching those, and deal damage to your opponent via lining up skulls. Victory is defeating your enemy before your own health runs out. It manages to take an already addictive formula and make it even more addictive.
I was first exposed to this game via the Nintendo DS game, and honestly think that the game is more suited to a mobile platform than to the PC, but the game is still a lot of fun here. Check it out if you haven't.