A classic case of unnecessarily trying to make something different and unique which didn't need to be different or unique.
Happens all to often. I don't think I'm alone in just wanting a story to stay the same just with high quality presentation instead of a new take on an existing story which was perfect in the first place.
Also, i know Yuji Horii and the creators of Dragon Quest games etc will have constantly heard from fans over the years how much the games have meant to them but to use that so openly as a major plot point is kind of like saying "hey look how great our games are". It's beneath Dragon Quest to "show off" in such a way and not something they have to publicise as the franchise is already so popular. Makes me wonder how much involvement Yuji Horii had in this movie as it really goes against his other work. I'm sure he must have signed off on the story though, right? Baffling. Maybe the "showing off" wasn't the intention and the writers were trying to pay homage to their fans support but it certainly didn't come off that way to me.
Anyway in my opinion the film was great up to the ending although i think it would work better as a tv series or a trilogy of films as a slower storytelling pace like the games have would work better.