IMO the reason videogame movies haven't worked..
I'm always a little annoyed when people make sweeping generalisations about video games 'not having decent stories' or similar when talking about the ongoing lack of success for films based on video games.
Personally, I think it's fairly complicated and as a gamer I've been annoyed at seeing the source material always cop the blame...
1) Cash-Grabbing
I feel most of the problems come down to this. Super Mario Bros was the first pioneer and really set the tone. SMB is blatantly not a project suited to a big budget live action movie, so making one is trying to fit a square peg in a round hole. There were certainly games that had better potential for adaptation, such as Secret of Monkey Island, but SMB was obviously a much bigger property that had made a lot of money and that's all that mattered to the execs who put a heap of money down for something unfilmable. Which relates to...
2) Indifference to the fanbase
This is improving, but was certainly a problem with those early efforts. You look at those first films that set the tone for what was to follow - Super Mario Bros, Double Dragon and Street Fighter, and it's clear that nobody was working on those films who really so much as understood the source material.
It should really go without saying, but IMO the first area that should be explored for a video game adaptation isn't even the script and storyline, but what the appeal of a particular game is. To use AC as an example here, I think one of the first things most people would say is a key part of the appeal is the historical setting, and right there you have the number one underused aspect in this film.
Notice that the FIRST adaptation to actually look at the reason the game was popular, to have the involvement of the games developers and to try and recapture it was Mortal Kombat, which was the first video game movie to make decent box office AND is still considered by many people to be the best. Period.
The indifference to the fans and their reasons for enjoying the franchise (even though replicating that is how you would make money) leads to...
3) Superficial adaptations
The real reason I get annoyed when people blame the games for having crappy adaptations is the simple fact that there have only been a few (but more now) that are genuine adaptation efforts. Famously, most of the films have put familiar names onto unfamiliar characters and run with it in strange directions.
I think this started because, yes, those early games were based off simpler properties - obviously SMB, Double Dragon and Street Fighters do not have particularly complicated plots (Although Street Fighter more than it's given credit for) - so the B-grade directors who got these projects because A-listers don't want to be associated with naked cash-grabs saw these properties as blank canvases to do their own thing with.
I feel it makes it a case of..
4) Self-Fulfilling Prophecy
The initial run of adaptations was so bad that its tainted the entire venture. Not just in Hollywood, but everywhere. You've probably seen it a dozen times on this board. Moviegoers, critics, actors, producers and directors are convinced that there cannot be a good video game movie. Many people have insisted that there will never be one, as if there is some irrefutable law that prevents it.
This has persisted in keeping A-list talent away from these projects, while the theoretically built-in audience has lured the struggling directors who want somebody to watch their films and want to slap a popular name onto their own crap. The Uwe Bolls come into play, with small names and big egos and entrench this further.
This has been so bad only a generational shift in Hollywood, of people who played video games growing up, has really altered the perception and gotten some A-list talent involved in these projects. Again, notice that the films which have A-listers on board have done better - Tomb Raider and Prince of Persia have been considered decent movies (baby steps) and Warcraft and Need For Speed were at least box office successes.
In the meantime games have evolved, and as far as I can see it has actually produced a problem that I believe to be the exact opposite of what people usually bring up..
5) Too MUCH Story to Adapt
I know a lot of people will scoff at this because 'video games don't have stories'. Um, no they do. If you think they don't you're living back in the age of space invaders.
A triple-A title now will aim for a solid 12-20 hours of gameplay at a minimum. That allows for a lot of dialogue, a lot of action setpieces, a lot of drama and conflict, a lot of backstory in often ancillary areas (ie reading journals, finding secrets) and generally its observed through the characters action. It's total immersion storytelling and is done effectively.
And yes, here I'm forced to agree with the snobs who say that video game plots are not ultimately mind-blowing. I mean, yes they are and no they aren't. The immersion effect when the game is done really well is about 80% of what's happening to you as a player - Half Life has a fairly basic sci-fi action plot. The appeal, especially in HL2, is feeling that you are LIVING in a sci-fi action world.
That said, I feel like the majority of films made now don't have mind-blowing plots so I think that's something of a red herring. No, the problem now is that the most successful games are sprawling franchises, with multiple titles of sometimes up to 40+ hours of storyline, multiple dlcs, expansions, tie-in books, comic books etc and backstory that ultimately informs a lot of the action and drama. More so than any other medium, video games NEED editing. And a lot of it - a $5 indie game like The Stanley Parable will take as long as a film to play!
To cut multiple hours of material down to ~120 minutes of screen time and try to preserve the action, drama, storyline and feel requires exceptionally good judgement and tact in editing.
As we have seen, video game movies have incredible difficulty appealing to any sort of star talent to join as a project, especially when it comes to the writers.
So those are my reasons why Hollywood Can't Make a Good Videogame Movie (rather than Why Videogames Don't Make Good Films)
I suspect the problem is that you have too many paperclips up your nose