I don't want to say simply 'no' in response... but.... NO!
Focusing on the title of the question:
Should the D&D Movie Been Serious - no, thank god it wasn't There is enough serious stuff out there. I wanted to be entertained, my wife (non-DnD player) wanted to be entertained, my three children (ex or current players) wanted to be entertained.
We were entertained. And what is it now $100million in ticket sales, positive review and good audience feedback suggests that other people were also entertained.
(Also, I was entertained enough to see it three times.)
or Not Called D&D? - no, D&D has clout at the moment, maybe only for a while but it has it at the moment. This was the perfect time to use the name and attempt to continue to build the brand.
SO where did it go wrong? (You didn't ask but it is helpful to consider this inline with my answers.)
Overspending on the movie and advertising.
I was thoroughly entertained but the movie didn't look like it cost as much as it did to make. Sorry but it didn't, less ego behind the marketing spend might have been good and perhaps they could have leveraged the fan base better.
All things to consider but I'm going with no and no in response to the question.