Just finished it for the first time. I have a fever but it kept me up playing all night... ugh. It's an adventure game that wants to feel like a movie, but with one major gameplay difference. Instead of getting to an area and being trapped there until you solve the puzzle within and are allowed to advance to the next area, like good old point-and-click adventure games, Heavy Rain constantly advances you to the next area (or scene) whether or not you've fully explored each area and solved whatever puzzle/ found whatever clues may lie within. This gives it a feeling of momentum which is new, and also really puts you on the spot when you have to make a life changing decision for a character in a way I don't think I've ever experienced.
It was a really satisfying thing to play through and I hope more games are made like this. I'd really like to see one that isn't about a serial killer, which is one of my least favorite themes. I'm impressed I was so drawn into the game despite that (I thought they kept the number of really creepy scenes to a minimum, and balanced them out with a lot of really interesting emotional scenes, which was nice).