This is one of my favourite films, and I now have it in three versions. I won't review the film as such, because others do it better, but mention has of course to go to the magnificent shoot-out. I could watch that again and again.
Anyway, to the blu-ray: The picture quality is better than DVD, but certainly not reference material. I was pretty disappointed by the sound, to be honest. I have a fairly decent system set quite loud, but found the dialogue to be quite indistinct at times. I also felt that the background music was simply too low in places. However, the shoot-out was pretty good, with glass tinkling at my feet, but the airport scene had the best effects, with massive LFE from taxi-ing planes and great directional effects from take-offs and landings.
Is it worth the upgrade? If you love the film like many do, you'll buy it anyway, as I did. I don't regret it, but feel that it can still get better, which means yet another upgrade in the future.