Some movies are so brilliantly crafted and lovingly made that although they have their origin in a book stand strong as their own complete work.
For me that is the test between the two, is the film complete despite the parts it can't include, does it draw me into the world or is it just a poor shadow of the world crafted by the book.
Bladerunner is complete despite missing such a quintessentially PKD aspect like mercerism and the empathy boxes.
On the other had lynches adaptation of Dune completely fails to create a complete world and really requires reading the book to understand its core and to feel immersed. (Still my favorite move tho)
If you haven't watched A Scanner Darkly you should that film is a visual master piece.
That's where I stand too. If the movie excels where it can in its storytelling, and brings its strengths to the table, then so be it. It usually makes for an equally powerful experience. I agree with the Balderunner example, and reasons stated.
I had forgotten A Scanner Darkly until reading a comment earlier, so I glad you brought that also. That one was brilliant, and the originality in how it presented the story was breathtaking. Given the subject matter i thought it was a clever idea.
But it pains me to see a great story wasted, or even ruined.
Thanks for sharing your thoughts.