First, a game needs to have a thorough and credible story to be made into a decent movie. I don't mean just a concept or even a cool premise... I mean it must have a solid plot with a gripping beginning, an intriguing middle, and a satisfying ending. The film must feature a believable protagonist fighting for justifiable reasons against a genuine villain.
Do you care to remember the worst movies from games? Alone in the Dark. Double Dragon. Postal. Dungeon Siege. Silent Hill. BloodRayne.
How about the best movies from video games? Mortal Kombat. Tomb Raider. Max Payne. Prince of Persia. Final Fantasy.
The best scores for a movie from a video game on Rotten Tomatoes are Final Fantasy: The Spirits Within at 44% and Dragon Age: Dawn of the Seeker at 45%.
To put this in perspective with other sci-fi and fantasy films.... the worst Harry Potter movie, Harry Potter and the Order of the Phoenix is 78%... the worst of Star Wars, The Phantom Menace is 57%... the 1978 Ralph Bakshi version of The Lord of the Rings is 50%... the complete and utter travesty that is The Hobbit: An Unexpected Journey is 64%...
And for the love of God... Snow Shark is only 42%... The Beastmaster is 42%... Hawk the Slayer is 58%... and the Total Recall remake is 47%.
Robot vs. The Aztec Monster is 50% and Yor, the Hunter from the Future is 51%... and they were lampooned on MST3K!
So do you really want Hollywood to ruin your favorite game?
I think that Bioware makes some games with good stories. Knights of the Old Republic, Dragon Age: Origins, and the Mass Effect series (right up until the end) all have potential to be told in another format.
My Commander Shepard was a paragon throughout the three games. He dispensed a ton of justice while showing mercy when he could. When the Rachni Queen finally communicated a promise to make peace, Shepard spared her. When any Krogan showed desires to live amicably with the galaxy, Shepard aided them. When the Quarians were threatened by the Geth, Shepard supported them. BUT... Shepard also backed the Genophage because the Krogan leadership continually refused to deal rationally with other sentient beings. His best friend was Mordin Solus. SPOILER ALERT. In the third game, when Mordin decided to undo the Genophage... Shepard was in a quandary. The Salarians offered their help against the Reapers, but only if Shepard stopped Mordin. The Krogan promised to help against the Reapers, but only if Shepard undid the Genophage. And since the Krogan race never repented the way the Rachni Queen did.... Shepard shot Mordin in the back and kept the Genophage in place. Then he lied to the Krogan by telling them the Genophage was undone. And he received full support from both the Krogans and the Salarians. I put the game back on the shelf for a while... I felt ill for two days after... And that was a gripping story.
Shepard was originally motivated by his desire to be the best, to make Spectre, and to help establish Humans on the Council. His motives became personal after Saren betrayed him. Then he found out the plan to destroy sentient life in the galaxy... and he found himself seeking some comfort in Ashley's arms.
And Shepard's life only became more complicated later, but the fuller story of the Krogan and the Genophage came out.
Harbinger, the Reapers, Saren, Kai Leng, and the Illusive Man make for a plethora of villains. Their morals and motives range from practicality and racism to greedy and sadistic. Add in the rogue Krogan, Humans, criminals, and Geth and you find everyone gunning for Shepard just because he's in the way.
The story had a solid opening and the tried and true premise of saving the galaxy. Along the way, the fates of several races were decided before the final battle even took place. Yet, the ending of ME3 was garbage. SPOILER ALERT. I was given three choices from which I could select to end the game. The first choice was to side with the villain of ME1. Wait... if I wanted to side with him, I'd have done it instead of killing him and thwarting his nefarious plan. The second option was to side with the Reapers, the real antagonists over the entire series. Wait... if I wanted to side with them, then why did I play well over a hundred hours of this game? I chose the option to destroy the amoral robots who tried to murder all sentient life. The writers deemed my choice as evil. Seriously. It was nonsensical, juvenile, and insulting. Kind of like having Superman travel through time by reversing the Earth's rotation or like having everyone in The Departed die as violently as possible in the last five minutes or like having Russell Crowe walk around in L.A. Confidential after being shot a dozen times.