I don't understand how they can turn comic book characters into good movies but not video games.
Comics are an established media, a cultural phenomenon.
The first movies based off of comics (in the 30s, 40s, 50s and even 60s) were very similar in treatment to video game movies today.
Also, comics tend to have established stories and characters and whatnot. The kind of games that movies are usually made from--action games--do not.
But the Mass Effect universe has plenty of depth already. A prequel novel and a sequel novel to throw into the mix as well.
It's also not strictly an action game. It's a space opera.