Puzzle Quest is a dangerous game. I thought it'd be a match-three game (like Bejeweled) with RPG elements, but I got it backwards; it's an RPG that uses match-three games to resolve battles. The design is smart and surprisingly deep. It's gotten both
classicaljunkie and I hooked. (Cruelly enough, the game card has room for two separate characters' save slots, allowing for exactly this sort of two-person trade-off addiction. Argh.)
Basically, matching jewels gives you mana, gold, or experience points, or hurts your enemy, depending on the jewels' color. There are also four colors of magic (tied to the four elements), and you can cast class-dependent spells if you can collect the right combinations of mana. (Yes, you have a character class.) The equipment you carry into battle adds various modifiers and bonuses, as with any RPG.
My favorite single feature: After you beat up a single type of enemy three times, you're given the option to try capturing it the next time you run across one. If you accept, you're given an actual puzzle to solve, where you have to clear the whole board of gems in as few moves as possible. If you succeed the beastie goes off to your pokedex dungeon, where (depending upon how many legs it has) you can try to convert it into a mount, or try to learn its spells. In either case you have to play yet more match-three games with different rules. This is why my warrior is presently loping around the map upon a giant rat. Its name is Bitey.
It's also got a Angband-like system of elemental-based resitstances. As you get deeper in the game you meet an increasing number of enemies who can pound you flat with some special ability that's tied to one of the four elements, and countering it means finding a magic item that grants you protection against that element. Unlike the formal, mission-based storyline, the game doesn't spell the solution out for you, and you've got to explore and figure out which shops or baddies are holding these trinkets, building your own dependency tree of monster bashing. Sadly, I am a sucker for this.
I can generally recommend this game to any Nintendo DS owner with either iron self-control or nothing at all to do for the next week or so.