They are two different types of games. Animation wise I have different expectations from both.
That said, I haven't been as impressed with Alan wake as everyone else seems to have been. It is still not out so I can't make any concrete comparisons.
From what I have read and seen Alan wake uses light as a tool to create atmosphere. For a survival horror genre it is essential to create a sense of dread and Alan wake seems to have it in spades.
Heavy Rain looks and plays completely differently since it is a different type of game. The atmosphere is created with the use of sound, camera angles and presentation (close up and panoramic view at the same time) more. A sense of urgency is introduced through QTEs that appear very differently than in other games. I played the demo and bought the game immediately. Since Quantic dreams now has the engine I hope they either make some CSI type games or license the engine.
Essay Pro