I would recommend Fahrenheit. It felt like watching a good movie, but that you could make the choices and outcome of every little detail in the story. It really reached a new level of interactivity if you ask me. The game has it weak points concering the story. The story loses a lot of interest close to the ending, but the game is definitly worth buying anyway.
Hm, I feel like installing it now. Come to think of it I really loved that game.
As I said, definitly worth buying!