NWD6 to me is just another cookie cutter skate/bike/windsurf film. The tricks are progressive and it's a great movie to watch and get stoked to ride.
The Collective (and from what I've heard, Roam as well) is more of an experience. The music, the cinematography, and the riding just flow together into an incredibly well rounded flick that encapsulates the soul of what riding is about to me.
If you're the kind of person who just wants to see people ripping off the flavor of the week tricks and charging hard to loud music, then NWD is probably for you. If you want something that you can sit back and get lost in for an hour, I highly recommend the Collective. Different strokes...