I believe Heavy Rain can still sell pretty well for a new IP in a uncommon genre whenever its released. The graphics, exclusivity and unique gameplay will help drive sales with the core PS3 fans.
That being said, release dates do matter!! I would not launch Heavy Rain on the same day as Modern Warfare 2 or God of War III.
I'm planning on buying it day one. I loved Indigo Prophecy (all the way up until the ending) and I had Quantic Dreams first game Omikron the Nomad Soul on PC as well. I'm definitely a fan of their work and Heavy Rain is one of my top 10 most anticipated games for next year.








