A great game explores a beloved subject and builds mechanics that are thematically coherent. As Rahdo observes, "what really makes Obsession shine is just how strongly integrated the theme is."
I can think of no better way to back up his words than to invite you to spend two minutes perusing the 28 page Glossary that comes with the game. The Glossary begins with a rich backstory, and then explores the role of theme in all game elements and mechanics.
Glossary Excerpt, Page 7
(Click for Glossary)
Only when game actions make thematic sense does that game have the rare potential to transport gamers to a unique time and place.