Most sequels refer back to their past "episodes", but they never alienate their audience by forcing them to play the one before. At this point, the prequel only becomes added story and background because the new story will fill them in on whatever details they need as they go along. The whole point is to get MORE people to buy the sequel and that means they need to treat the new game as if it were a new game and not a sequel.
So, with that being said...IF you're really wanting to know the backstory AND if you have the funds, then go and play the original first. I see no problems playing the new game, then going back to the original when you have the time. If the game makers did it right, then it shouldn't matter which game you start with first.