Pretty much any successful book or game is seen as a potential movie franchise these days. Some novels seem to translate well into movies, others don’t. Even for successful debuts, there is at least one fan of the original out there somewhere who hates it. Video game adaptations seem more cursed than the Defense Against the Dark Arts position, and infamously, not one movie based on a game has managed to achieve a “fresh” rating on Rotten Tomatoes.
Why do cinematic adaptations go wrong? For one thing, people producing them often appear to not have much sense for what makes a medium work. Different mediums have different strengths.
The strength of writing, prose or poetry, is that it suggests things to your imagination. Any time you read something, the writer is only doing part of the work -- you’re filling in the rest with your experiences, memories, phobias and dreams. This is why, while there are good and bad pieces of writing, you have to invest yourself in a story and read it with intention if you want it to affect you. A writer is, in a sense, using you as material. Poems or novels can be so powerful because they are such intimate experiences. If a book happens to access the right parts of you, you can have a deeper experience of it than the person who wrote it might have even thought possible.
The strength of a movie is that it is a combination of numerous art forms -- visuals, music, acting and writing, and this combination can produce a potent experience. While there is room for a movie to connect or not connect to you personally, there’s less -- a movie is about the filmmakers overwhelming you with their vision, rather than letting you have your own. Usually, a movie adaptation of a novel is only successful if the director's vision of the story is richer than yours, and replaces it, or if the actors succeed in embodying the characters so well you can't imagine anyone else if you give the book a re-read.
The strength of a game is that it is an interactive experience. A movie adaptation of a game takes the game part away, leaving only the story, and in the case of most games, this isn’t a good thing. Stories in games are often simplistic, convoluted, or derivative, because they're generally furniture and don’t really need to be anything else.
This might be why some argue video games can’t be art, because A, the conventionally “artistic” elements -- story, visuals, music, writing, etc., even if well constructed, aren’t the “purpose” of the game -- the interactive challenge is and everything else is just peripheral and decorative, and B, the fundamental interactivity of games can cripple an attempt to provide an emotional, artistic experience with these elements. If there’s a really touching, poignant moment in the story, for example, you can make it ridiculous by jumping up and down, dancing, moving the camera around, repeatedly shooting the non-player characters, or abruptly jumping into a lava pit. Others might argue in response that some amount of the experience of any work of art is in the control of the viewer, but that’s a debate for another time.
Some games, the ones often cited in response to the claim that games aren’t art -- "Bioshock," or "Shadow of the Colossus" (which does have an adaptation scheduled) could make potentially decent movies because their stories, themes, or imagery are as or more memorable than their gameplay.
This is why when adaptations are made, they should be seen as a "new' work of art that re-purposes elements of what inspired it to create something different, because each medium of entertainment is its own untranslatable language.
