I think this thread is the very same thing as those people dissing books by saying "I'll wait for the movie".
Truth is that (comic) books, video and games (among others) are types of medium. Changing from one to another can be easy or hard, but even the easiest transition is perceived DIFFERENT because of the way the medium presents the narrative to the audience. And of course there's the obvious: it's not because someone can make a good game that they have the means, knowhow, ambition or the vision to make a video of it.
...and I assume this is all pretty vague. Let's get some examples in here, myah?
-The walking dead. I've read a lot of the comics, a couple of the series and the first season of telltale's one had me almost crying. The differences in how much I wanted of it isn't in the lore or narrative (while different, they have the same mood and idea going), but in the matter of investment on my end. When I watch the series, I see people doing things, but I just couldn't bring myself to really care about the protagonist or anyone else. The comics had me interested because the black-and-white pictures with sharp dialogues made me care about the world. However, the telltale game made me care about the protagonists from almost the get-go. Even if those first choices mean jack shit (I totally forgot what I had my character say to that agent who was driving him), I didn't knew it at THAT point...so in choosing an answer, it was more MY persona than anything.
-gone home. Or most other walking simulators. While this all can be done through film, the very fact you have to read and listen to voices of things makes you invested. Any seasoned film maker can tell you that a movie in which the protagonist does nothing but open letters and hold them to the screen is going to be boring as hell. Also: what you show and don't show matters a lot in a movie (see also: alien or jaws). This game would never be as captivating if you could actually SEE the characters. The very fact that this game goes around this establishes the player himself as part of the story.
-song of saya: my example of a graphic novel. This same goes for 999 or (I guess) Ace Attorney, but Saya is interesting in that it has but 2 or 3 choices to make throughout the game. Meaning: a novel far, far more than a game. Nonetheless, the fact that you have to make these choices (and they directly reflect the changes) justify the reason of it to be a game by itself.
As for games that
should have been I'm interested about when talking about a hypothetical movie:
-999. I admit I have NO IDEA how to make this a movie or a series, but I'm interested. A lot.
-firewatch: yeah...I know this one gets one. And I'm more interested to see how this turns out than that tetris movie (my guess: better)