The Negotiator presents us with both of two things in a summer full of flicks only containing one or the other: ambition AND intelligence. It doesn't have any qualms with taking a far-fetched concept and treating it with absolute seriousness, but unlike most movies that are willing to do this (especially some recent ones involving very large asteroids and very large lizards), it is able to pull it off by combining a tight script with strong, strong acting.
If this were a perfect world, Jackson would deserve an Oscar nomination for his performance here. There's no way on Earth he'll get it, of course, but he's given the difficult role here of playing a guy who has to convince the guys downstairs that he's a psycho, while convincing the guys he's kidnapped that he's innocent, and he does a flawless job of it. No easy task, especially when you consider the fact that he's got to throw in the occasional gunfight. At least he'll probably win the MTV award :)
What results is a skillfully made film. I enjoyed it. It made sense but kept me guessing, the action was intense but still followed logical patterns, and the ending was not a disappointment. An altogether fun experience.