This game came out while adventure games were still trying to figure out how to handle 3D and it took a very unique and awesome approach. You control the camera in the scene - I mean REALLY control the camera. Gabriel or Grace (the main characters) are still controlled via the traditional 'point-and-click' interface, but you're immersed in the world with them this time - able to navigate around w/ the WADS keys and modifiers. It all works remarkably well and is a highly enjoyable experience.
Especially with today's beefier graphics processors, I wish more new adventure games would go this route - the camera control absolutely adds something to the game... it's what pushes it from a 4 star game to a 5 star game.
Even without the camera - this game is fantastic... (mostly) good puzzles (***mild spoiler alert*** look up a walk-through for the cat-hair mustache puzzle in the beginning of the game to avoid pain), great story line, and fantastic character development. Highly recommended!