Honestly, they shouldn't make a Halo movie about things that have already been made into games. What they should do is take a few of the books and make them movies. Movies based on books aren't usually horrible like most movies based on games. They could even do the movies in multiple parts so they could be more descriptive, and people would still go see them. I'd honestly rather see a 3 part tFoR then sit in the theater for 3 hours anyway.
Also, Microsoft should give a bit of leeway. For the books, the contact the author and say "here's an outline, use your imagination." I know why they can't be THAT lenient with the movies, but it makes no sense to be as strict as they were.
Also, there is a group currently working on a Halo movie, nonprofit. I'm not sure how far they've come, but they are working on it.