I personally would have liked to have seen **** Grayson's journey throughout a number of movies, Batman1, Teen Titans, Batman 2, Nightwing, etc. Titans tv show just doesn't get the exposure a motion picture would for him. Still waiting on a Justice League Dark too, but looks like J.J. Abrams is ready to ruin that franchise now too.
I agree that you have to go Marvel's route - build the foundation of a major character in their own film, then you can cross them over. Got to establish why you care, not just throw them in together and expect you to know them.