In my honest opinion, DoC was made with good intentions, and was promising, but kind of fell flat. First off, and this is purely my though, it was a shooter, I hate and am terrible at shooting games. That made it incredibly frustrating.
Is Vincent terribly interesting in FFVII? No, but how could he be when there was a chance you never even met him in the game. However, his story, with relation to lucretia and Sephiroth were very interesting and answered a lot of question regarding what kind of crazy people decided to create Sephiroth. Also, who else were they going to make a sequel of? Tifa? pleaaaase. Barret? Wouldn't waste my money.
As far as Weiss? He could have been cool, had square bothered to build on him AT ALL.