I don't know if I am "most people" but I don't dislike Uwe Boll because it's fashionable to do so. I dislike him because he butchers an artform and doesn't seem to care if he does so. As an aside, although many of the games he adapted aren't ones I'd play, your evaulation of the games as being "stupid to begin with" is very subjective. Even if everyone on the planet literally agreed with your assessment, it's irrelevent since he makes no attempt to work with the material he's adapting. Although I don't know the man, I also disagree with your assessment of the man. Someone writing fanfic has a love for whatever they are writing about. I see no love of such coming from Uwe Boll, I just see someone milking a license for all it's worth, bleeding it dry.
As an aside, you almost seem to forgive Uwe Boll since he's making films out of games you deem stupid with vapid storylines. Would you forgive him if he made a film about a game, book or something else that you didn't find stupid and/or vapid? Again, your assessment of stupid and vapid is subjective. For many, they might not feel said games are stupid and/or vapid, and might be honestly offended that such a horrid film was made about a game they enjoyed and cherished.
Or to put it another way, it is possible to dislike the man, even if he's adapting what you deem to be vapid stories, for butchering an artform. He also has done work that wasn't adapted from any game or any other media and butchered it too. If someone's initial dislike of his work came from seeing one of those films instead, would their dislike of him now be valid?
I guess I won't make assumptions as to why people dislike Boll, especially based on subjective anolysis of the material he adapts. If you wish to do so, fine. I know why I dislike him, and I find my reasons valid. I know I'm not on some "hate Uwe because it's popular to do so" bandwagon.
You're making the assumption that a game's being stupid and/or vapid automatically qualifies it in my mind as being a worthless game. Take for example my favorite game (aside from Fallout 3) which came out of 2008... Saints Row 2. I love this game almost as much as I love a fresh BLT in the morning. The game is incredibly stupid, juvenile, and ridiculous but at the same time is the most fun I've had with a video game in a really long time. I also had a very similar experience playing the original Alone in the Dark, House of the Dead, and Bloodrayne. In fact, I loved Bloodrayne (the game) quite a bit BECAUSE it was stupidly violent and appealed to my inner 13 year old with all the briasts and "GI Joe's-in-the-backyard" storyline. Now let's say Saints Row is up for a movie deal; It wouldn't matter if it was directed by Uwe Boll or Brian de Palma... it would be an awful movie. There is nothing remotely cinematic about it, and in order to make it cinematic you would have to alter the concept so much it would cease to be truly "Saints Row".
I don't disagree with you that Boll is shamelessly cashing in on franchises and ultimately making awful movies of stupid, but fun, games. My problem comes from the fact that in any Uwe Boll thread that pops up we have posters who will make it seem like Uwe has used the Holy Grail as a toilet and the Mona Lisa as toilet paper when that simply isn't the case. Even if we sat down Spielburg, de Palma, and Oliver Stone to work on it there would no way they could make House of the Dead or Bloodrayne watchable while simultaneously maintaining faithfulness to the game itself.
I suppose what I'm stabbing at here is that video games, in general, make awful movies. It doesn't matter if it's Uwe Boll, Paul Anderson, or my own Speilburg/de Palma/Stone fantasy. Fallout is no exception. Fallout has always been, essentially, half parody and half homage to movies that already exist. To make a movie about it, regardless of the director, would result in a highly derivative and uninspired movie. The only way it could be spared of that fate would be to have an almost entirely original storyline which moves away from what was presented in the games, and at that point it would be difficult to be recognized as definitively Fallout at all.
tl;dr
Is Uwe a shamelessly bad director? Certainly.
Are his movies unbearably awful? No doubt about it.
Were the original games touchstones of their genre? Let's not get too hasty...