Puzzle Quest

Puzzle Quest is a rather frustrating game: the graphics are terrible and the game is buggy and crashed frequently* -- a rarity for a console game. But it's also incredibly addictive. There's a veneer of an RPG game bolted onto Bejeweled as a battle mechanic (and item-forging, spell-researching, etc. mechanic). Something about the near-mindless pattern matching combined with the "I'm making progress" of the RPG system combined to keep me (and Erica) playing the game for months. When I hit a brickwall at the final boss, even after completing all the side-quests, Erica helped me grind through enough battles to get enough gold to improve my stats to the point where I could beat Bane. And now that the game is finished, Erica is still playing to finish researching all the spells.

I did have a pet peeve with the intersection of the story and game mechanic. It was incredibly unrealistic that you could capture and control entire cities and it didn't affect your relationship with the inhabitants at all. I realize I'm making that complant about a game where this is high battle, but still.

* Fortunately the game auto-saves after battles, otherwise it would have been thrown out the window in frustration.