Plot
Not a lot of information has been released, but we can piece together a few things and also add a bit of speculation.
Dark Shadows started as a daytime soap opera, so the plot had to be the perfect balance of simplicity and complexity. Even from its very first episode, Dark Shadows focused on mystery and suspense rather than the usual tragedy, complex revelations and tera-jerker stuff that traditional soap opera programs had relied on. That in itself set it apart, but the series took on a life of it's own when the ghost of Josette Collins appeared. Then David's mother the Phoenix and finally the arrival of vampire Barnabas Collins.
The Barnabas Collins storyline proved to be so successful and resonated so well with audiences that it became the main plot for the first Dark Shadows movie. This is essentially what we should probably expect for the new movie as well.
We'll probably begin by establishing the Collins family as being wealthy and having a long history, and we'll probably see young David's morbid curiousity. In the show and movie, we see Barnabas being set free from his grave but this may not be shown in the current movie. Mysterious cousin Barnabas will arrive, and everyone will notice how much he looks like the "original" Barnabas collins, who lived 200 years ago. Little do they know...
We will probably see a lot of Barnabas and get to understand both his good sides and evil sides. Even though he commits cruel acts (murder, turning people into his zombies), he's burdened with the fact that he lost the love of his life many years ago, and dating is a bit hard seeing as how he can't see sunlight and he's the undead.
In the end, will good triumph? That is something we'll just have to wait and see!