I don't really care.
The story in Halo is no worse then your average "sci-fi" movie these days, with pretty clear conflict and conveniently labeled bad guys. Modern CGI can obviously take care of all the inevitable fighting and science fictiony stuff. The setting is basically already there from games...
It only comes down to plot, and frankly I don't think it would be that hard to come up with a storyline that's based in the same setting as the games, has some kind of significance to it, and can be wrapped up in 2 hours or less.
So, theoretically speaking, there's nothing impossible about it. Hell, it could even be good. Although, given my general cynicism and neutrality to game-based movies and Halo series in general, I don't know. But, you know, all the framework for a fairly successful movie is already there, same thing counts for quite a few of other game-based movies that flopped.
So I can't really say why they end up fucking up every time.
P.S. Master Chief doesn't even have to be the protagonist, y'know? If you're interested in saving his formidable lack of character. Which kind of applies to Gordon Freeman as well if you think about it, hur.