I just watched Knockin on Heaven's Door last night, which highlighted for me potential problems in the live action movie. I don't think bad acting, bad dialogue, or even a bad script would ruin the movie. Lack of stylization would kill it. The worst thing that could happen to this movie would be a soundtrack containing no jazz. Also, Keanu Reeves needs to spend most of his time not talking.
Instead of recapping the whole show into 2 hours or continuing it, they should do what Knockin on Heaven's Door did - make a new, long episode placed somewhere in the series.
I don't think he would work very well in a live action movie.