Puzzle Quest is the most addictive game I've played since Civilization 4.
I wouldn't have bothered with it had it not scored an impressive 87% in April's PC Gamer (making it the highest-scoring game that month) and attracted the mag's infrequently-seen "Must Buy" award too. It's only $20, and is available on Steam, so I decided to take a chance and download it. I'm glad I did.
It's a cross between Bejeweled (a popular casual game that I've never played) and a role-playing game. You take the role of a fantasy hero trying to save his homeland from an undead invasion by doing quests and fighting monsters - with all combat being resolved by playing a turn-based puzzle game. The puzzle consists of an 8x8 grid containing coloured icons, and each turn you have to swap two to try to make lines of three or more identical tiles. Depending on the tile icons, you either gain mana, gold or experience from the match, or cause damage to your opponent. Mana can be used to cast spells with a wide variety of effects. The first person to reduce his opponent to 0 health wins the combat.
It sounds simple, a little dull even, but it's very strategic. In addition, there's a variety of other stuff layered on top, from mounts, to special items, to crafting and spell creation (done via mini-games that are some variant on the combat puzzle game), all of which confer various bonuses and extra abilities in combat. It all makes for a surprisingly rich experience.
It's also nice to be reminded that great games don't have to have first-class 3D graphics and computer-melting minimum specs. Highly recommended.