OMG are people actually comparing the thousand page Tolkien literature with Halo the video game? The one with a hundred million fan base? There's simply no comparison in terms of risk and name recognition. The university I went to even had the entire section of dormitaries named after locations in Middle Earth. Look it up, it's even in California and not some obscure rain forest.
When you look at the movie industry as a whole, for each good or successful movie (not necessarily the same thing) there are 10 bombs. More often than not, and increasingly more so nowadays, the good movies are based on existing works, or from original scripts that have only been greenlighted at several levels, passing certain standards. That is why till this day we still do not have an Ender's Game movie, because there hasn't been a decent script for it yet. When someone insists on making a movie based on a video game and want to "rush" it out the door by 2008 summer, instead of waiting for the perfect script first, odds are stacked against it. Not saying there's no chance for it to be decent, just not likely that's all.