I'd watch it, as long as it had unknown actors, and (hardly any) CGI.
That. I like when no-names get to shine. I like Sharlto Copley in District 9, I like Christoph Waltz in Inglorious Basterds.
I also hate CGI, at least when you almost base a movie on it. Ugh for Avatar... Sci-fi Pocahontas with pretty graphics.
I'm ok when you maybe CGI-
enhance effects that you had when you filmed a scene.
I think film makers should do as much as they can with trick filming, make-up, dolls et cetera, before they need to go to CGI.
I notice more and more movies where something as easy as blood is CGI. A bullet wound, a little splatter. It looks bad, use fake blood, make-up and a pump to make it gush.
Then it shouldn't be a movie, either. 90-120 minutes is too short time to tell enough about Fallout for a newcomer, and to cover our needs for lore, story and canon.
It's this thing, that I think most game movies do and that many people may hate, that the movie should have an unique story from the game. If you try to adapt the game's story to the screen, people will complain "you made that wrong, that thing is against canon, you didn't include that part and who the hell is that?!" The same story ain't gonna be the same, and you'll be ticked off. Unless it's a really pro film maker that can please us with other parts. But all I ever see are people bashing films adapted from games.
That's why it should be a TV-series. 45 minutes/episode x maybe 16 episodes/season = 720 minutes. That'll be plenty to cover Fallout, to include everything in the story that'd make us happy. Then you also have to think of the film maker's needs to do something different, to use his fantasies and add new things. Or rather the people who write the episodes. They just don't want to copy the entirety of Fallout, turn it into a film. They want to use their own ideas and put them in somewhere in the production, in the already existing story/lore. Kind of like the series The Walking Dead. I've read most of the comic books before it turned into a TV-series. It follows the story pretty good, but many things were changed and many things were new that they added. If it was a copy of the comic, then I'd know everything that's gonna happen before it does and that ain't fun, is it? I still kind of do, though, but I never expect these new things that pop up.
What I would like, though, is that if they made a unique story anyways, as a series. Maybe put it between Fallout 1 and 2, telling the stories of a bunch of people that aren't even in the game, but how they live in the Fallout world with things and people that are in the game, like the NCR with Tandi as president. There'd be New Reno with mobsters and drugs, Broken Hills and Marcus, Vault 13 and 15 or just the mention of them, Vault City with the [censored] First Citizen Lynette or maybe her predecessor. San Francisco and maybe the Shi, even? Tribals, raiders, dark humor, drugs, six, gritty wasteland, violence... references to the games all the time, maybe mention of the Vault Dweller.
Note, that if that series would take place between Fallout 1 and 2, it would most likely follow Fallout 1's canon the most, and break some canon of Fallout 2 because the characters need to be interesting and may effect things in the world that would have a different outcome in Fallout 2, maybe messing with the families in Reno, helping Broken Hills or whatever... Unless the film maker is really good, has played the games alot and love them, and is flexible with his own story and the games, so that they won't contradict too much and still be very interesting.
Otherwise, the easy path - series takes place, err, after New Vegas. But I rather have it closer to Fallout 2.