Let's face it, Spawn the comic was never going to be easy to transfer onto the big screen.
I think that Todd McFarlane & co didn't do all that bad a job of the movie, however, I do believe that the movie could have been MUCH better than it turned out. If only they made the film darker, like the comics, more in the style of say "Blade" with Wesley Snipes.
A great prospect that was never given the right script, actors or director, Spawn could have been so much more than just another action movie with some eye-catching special effects, but alas it isn't.
Although Michael Jai White wasn't a bad choice for Al Simmons, Tony Todd should have been brought in for the voice of the deceased Simmons, aka Spawn. Also, someone like David Fincher could have directed this better in my mind and Todd McFarlane could have co-wrote a fantastic script with someone like Kevin Smith.
I have heard rumours of a sequel, which is promised to be a LOT darker than this, the first Spawn movie, I hope this is true, as Spawn really deserves to be a big budget, cleverly scripted box office & critical hit of a movie, not this half-... attempt.