I can't imagine this being good. But here's hoping!
I'll elaborate on this. What makes Dragon Quest good, at least to me, is the feeling of the game world. You get to this by exploring and fighting, yes, but mostly you get to it through talking to people. Now, of course you can make a film based around people talking to each other engaging, but it's a harder sell for an animated feature, especially one aimed at kids. My worry is that this will be too action orientated.
Really, to do the story and the scope of DQV justice you would need a TV series or a number of films. Part 1 dealing with the hero's early life and trails, part 2 adulthood and so on. This could very well be the approach that the filmmakers are taking, I'd certainly hope so, anyway, colour me cautious for this one.