In fact, according to screenwriter Mark Verheiden, the movie will be decidedly darker; a little like the popular Batman Begins. At one of the panels that he appeared at he commented that "It's not light and frothy. It's not silly. I want to play the characters so they feel real to us, not like people we can't understand. And I think Nightwing is a great character for that.”
Fans of the Teen Titans like myself are no doubt ecstatic with the news. For me in particular, the fact that he has linked Nightwing to the darkness bodes well for a realistic Teen Titans movie, and one that will no doubt increase the franchises popularity.
For a look at the full after-panel interview that IGN conducted with Verheiden, then check out the link below. He is commented on the feel of the movie, and his own personal influence, in particular his love of Marv Wolfman’s writing of the Titans.