It depends entirely on the specifc game and what you get out of them. The Witcher games are story-heavy and would have enough content to fill a long-form series, and people who play for the narrative would likely enjoy that.
But then there's something like Hitman. They've adapted Hitman into a movie twice and they keep getting worse at it because whoever's making these movies has failed utterly to understand what Hitman is like to play. It's, arguably, unabaptable. A television series would possibly work better than a movie, but even a series would struggle with the same problems. Producers see a game about a badass assassin with a story that involves human cloning and plots for revenge and they just think "cheesy action movie". But Hitman isn't an action series. If you play it "right" there'll be very little action at all. The less the better, if anything. Hitman is about trial-and-error, investigation, patience. It's about playing a single mission over and over and over and over and over again, learning maps and AI routines and item locations and how all these moving parts interact with one another and how you can manipulate it to your ends, ultimately for the purpose of doing as little as possible to make small but specific imapct on a given level. In some regards Hitman is similar to a puzzle game. That experience can't be translated into a movie, or a television series, because it's not narrative. Hitman's story, like most stories in video games, exists to give context to gameplay, nothing more. In fact, the one time Hitman tried to tell a complete story everyone hated it and said it ruined the game entirely. And it did. Absolution's greatest weakness was that it wasn't a series of "puzzles" like Blood Money or Hitman™.
Another thing to bear in mind is that just because a game can last for twenty hours doesn't mean it has twenty hours worth of story content. How many games with play-times in the double digits are only two hours long when all gameplay is cut out? Many games these days are still trying so hard to be movies that the gameplay and the narrative are almost entirely divorced. To use a simple example, look at Groose in Skyward Sword. He has one scene where we see him as an arrogant jock, then, many hours of gameplay later, there's a scene where he sees the Surface and suddeny he's not arrogant anymore. Such good character development. Groose's arc takes place over two story beats which last for about ten minutes total. Having eight hours of killing bokoblins between those beats doesn't mean Groose had eight hours (eight episodes, say, if it were adapted it to a television series) of character development.
I think it's a mistake to believe that video games can all be adapted to other media. Many can, more so these days since video games have tried so hard to emulate movies in recent decades, but there's a fundamental difference between video games and television or film: Video games are not only about storytelling. Many people, yourself included, Deus, primarily play games for story, but they are not primarily made for that reason. Otherwise they would be movies. The Witcher began as a series of novels because Andrzej Sapkowski wanted to tell a story. They were adapted into video games because CD Projekt Red wanted to make a game. If they only wanted to tell those stories they would have made a movie or a series instead.
Books, television, and film exist for the exclusive purpose of telling stories. Video games exist for the purpose of being played. You can tell stories while doing that, the two aspects can work together to make an experience that excells beyond other media, but that difference is crucial to the success or failure of adaptation. If a game has a strong narrative element, and if its audience is strongly invested in that aspect of the game, then adaptations can work. The Witcher would probably work very well as a television series. Halo would work well as a movie. The Elder Scrolls would work well as novels. But many games just won't work because the game itself is focused on gameplay. Super Mario Bros comes to mind. Hitman, as I spoke of above.
As I said, it comes down to the game in question. Are its narrative elements developed enough to sustain a narrative-only adaptation? Is the audience invested in that narrative enough for the product to stand without the gameplay? If the answer to those is yes then an adaptation could be successful. Whether such a thing would be better as a movie or a television series comes down to the nature of the given narrative. Sticking with the above examples, Halo could be a movie. It's a self-contained mystery story that could be condensed to a two hour movie. Something like, say, Oblivion's main quest would be better as a television series because that form would give enough time to build the world so the audience could understand what was going on, as well as developing Martin Septim from a sheltered priest to the man who would channel a god to save an empire from an invading devil. Top lad.
As for adaptations I'd like to see, I wouldn't mind seeing a Dishonored movie. I love Dishonored so there's that, but I think it could be very visually exciting with the right director. I do say movie specifically, I think Dishonored would work better as a film than a series. A series would have to stretch things out too much and I think it would drag. It's fine playing the game for twelve hours because I'm doing stuff, trying new plans, engaged regardless of story. But there's just not enough narrative content to fill a long-form series. Corvo was wrongly accused and seeks revenge. Sick. Maybe he decdes to show mercy. Cool. You can do that in two hours.
I also wouldn't say no to a somewhat low budget Resident Evil movie. One that actually takes place in the mansion and isn't an action movie, but rather a slow-paced atmospheric thing. Given to the right director, you could make a film that's intense and haunting and did the game justice. Again, a movie because a series would just drag things out and wind up full of filler. Later games could possibly work as a series, like Resi 5 or 6 (the Revelations games are structured episodically, as it happens), but the original game is movie fodder in my opinion.
