Saw a cut/paste block of text taken from the IGN review and after reading thought it was worth posting here. no spoilers here. just a brief outline of what to expect - basically 'this game will be slow to start and then pick up'
"February 10, 2010 - If you're planning on skipping the bulk of this text and heading straight to the review score to decide whether or not you should play through Heavy Rain, just know this: the game starts slow. It'll take you a couple hours to get into the meat of the experience and for things to really pick up, but once it does, you'll be on the edge of your seat until the end and you won't want to put the controller down. In other words, if you stick with it, Heavy Rain will give you a ride like you rarely see in games. "