As far as the idea that you can't do "D&D" as a movie, I would point to several popular movie titles that have certainly started with less. Pirates of the Carribean is based on a, what, ten minute Disney World ride. Disney's taking another swing at the cat with Tomorrowland. Not sure how well it's doing, but, it's certainly being tried.
D&D has a mountain of built in flavour to use. No, it really isn't "generic fantasy" and, as proof of that, I point to how hard it is to actually mold D&D around existing fantasy worlds. D&D does a terrible job of Tolkien's Middle Earth. Trying to do Game of Thrones in D&D is an exercise in frustration. So on and so forth.
Earlier someone said that Harry Potter isn't what they want to see. But, honestly, I think as far as the world goes, Potterverse is probably closer to a D&D world than Conan. Revel in it. D&D is pretty high magic - so, make fantasy worlds where magic is everywhere. Keep it in the background, similar to the Star Wars movies. Heroes are walking down the street and see a cart being drawn by giant beetles while a procession of priests are being carried aloft by flying whosits. Magic stuff all over the place. If they do a "dungeon crawl", which, in a D&D movie, they probably should, then Hogwarts should be the inspiration - floating stairs that move, talking statuary, ghosts, etc.
IMO, that's how you differentiate a D&D world franchise. It's not just a Medieval world with a bit of magic, it's a Magic World set in a medieval period. Dragon born were mentioned earlier. Why the heck not? That's a purely D&D race, one of the very few. I'd expect to see Dragonborn in a D&D movie. Easy action figures and they look cool. And you have the added bonus of not being another Tolkien rip-off.
I mean, if you do the typical setup with an elf, dwarf and halfling, it's too derivative. All the "standard" D&D races are yanked straight from Tolkien. Why not actually use D&D races in a D&D movie? Main guy is human, but, his buddy is a dragonborn. What's the problem?