I know some people have had mixed feelings after playing the two-level demo of "Heavy Rain", but after having completed the main story mode, I can say this isn't a game that is going to wow you in a short demo. It wasn't until about halfway through playing that I was seriously engrossed in the game. "Heavy Rain" doesn't just give you control of a character, it forces you to become that character, giving you an attachment that most games could only hope to replicate. Sure, some of the actions may seem tedious, and some of the chapters at first don't seem to have much of a purpose, but this isn't a traditional platformer, where you complete a task and advance. Sometimes the task you complete is only there to give you better perspective on who you are and what your character motivations are.
The primary story of "Heavy Rain" features the Origami Killer, who has kidnapped the son of Ethan Mars. Throughout the game, you'll control Ethan and others as you try to identify the killer and rescue Shaun before he dies. Because of the way the game established Ethan and his relationship to his son early on, I quickly became motivated to save him at any cost. The amazing thing is, because of the level of engagement with the characters, my emotional response often mimicked that of the characters on screen (particularly when Ethan is asked to kill a man to get another clue toward the location of his son).
Mechanically, as I mentioned earlier, the game strays from the traditional mode of "X is jump, Circle is talk, Triangle is action" for controls. Instead, you're presented with on screen prompts that either direct you to press a button, make a motion with the right analog stick or move the sixaxis controller in a specific way. At its core, this turns the interactivity part of the game into a series of point-and-click actions or quicktime events, but somehow it works. The control scheme shines during the intense fights, where the on-screen prompts flash quickly and have to be completed to prevent failure. In games like "Heavenly Sword" or "Force Unleashed", the QTEs take you out of the moment, but because of the rapid-fire direction of "Heavy Rain", they serve to keep you intensely focused.
Because "Heavy Rain" is so different from most games out there, there are definitely some people who may not like it. But for those that do find enjoyment in this experience, the trophy system and multiple endings (reportedly, there are 8) will keep you engaged well past the point of initial completion.