It actually is a good movie. Unfortunately, to get it down to 137 minutes, Disney had Hancock trim too much out of it. This movie easily could have been the three hour epic that was originally envisioned. There's a couple of scenes that may not make a lot of sense to people to people not familiar with the subject matter. I read the novelization of the script and there's a couple of major, and a few minor, scenes missing.
As for not doing well at the box office, that seems to happen when the doom and gloom predictions start long before the movie comes out (there is the rare exception, like Titanic). Disney didn't help by announcing a Christmas 2003 date then pulling it. Whenever that happens it always gets the rumor mill going. Going up against The Passion on Easter weekend probably didn't help much either.