Counterpoint-
Pirates of the Caribbean (Based off of a Theme Park Ride)
Transformers (Based off of a Toy)
I could keep going, but you get the idea. Here's the thing, IMO. Movies are a different medium. I mean, sure, some sources (books, comics) are a little easier to translate to film, but ... it's still different. And that's before you get to specialized use cases (such as Tristram Shandy, or Naked Lunch, both of which have ... movies ... that are good, but are very different than the books).
Any movie as D&D is not going to even attempt to be D&D qua D&D. Instead, it's going to try and (hopefully) be a good movie, first. And saying that you cannot find good characters somewhere in the history of all the D&D is, IMO again, preposterous. At least in comparison to Pirates.I mean .... there's been books, and stuff.* Narrative books, you could buy in the fiction section of a bookseller.**
So D&D does, in fact, bring a lot to the table. It brings some built-in knowledge. Both the actual players as well as a general level of background knowledge (if nothing else, someone might remember it from Big Bang Theory to Stranger Things or from seeing something something youtube). It has a decent cachet in the creative community, which is always a small bonus when bringing something to screen. And it has a rich and storied set of ... stuff ... that can be used, from Mind Flayers to Beholders to FIREBALL!
*Maybe a lot of them weren't good. But there were a LOT of them.
**To the extent it hasn't been killed dead by Amazon.
Good points, I agree with most of them.
However, I'm curious about which novel series you think would be a good movies or series of movies?
I don't doubt the quality of D&D fiction, I'm actually curious.