I've heard it's a mix of Heavy Rain and Red Dead Redemption. I haven't played Heavy Rain yet, so I agree with Pootie that I need to try that first to make sure I like this type of game.
My only fear is that it might be too repetivie - investigate crime scene, interrogate, shootout, case solved. I trust Rockstar so I'm sure I will be picking it up sometime (unless the review are awful). I have a huge back log of games rignt now so I need to resist picking this up right away.