I've never read the Tarantino script, so in all honesty I can only reason how his script was by the story, deleted scenes that I know he wrote, and Qt's style contrasted with Stones.
That said I'm one of the few who loves Natural Born Killers the movie, I think it's entertaining, very creative, and a landmark film. I can understand why some hate it though, I did the first time I saw it, but later grew to love it. As far as where the movie stands up against QT's, I think it's really the only one of Stone's that is as good as most of Tarantino's.
Now if Tarantino directed the movie with his own script I would probably love the movie just as much, but it would be a totally different movie (script or not, the style would be completely opposite). I think alot of you are forgeting that these two are totally different directors, who make totally different movies, but both are original and exceptional in thier own ways.
Now as far as Tarantino being pissed, I understand that, but there is probably alot of personal baggage in that. If you invested your hard time in a story and in the characters, and basically had to sell it to some guy who decides that story doesn't suit his style, and to change everything around, you'd be a little pissed too. But as a director is it really a good thing to go shot by shot what someone else wrote down, when you personally feel it should be in another direction. Obviously Stone loved enough aspects of the screenplay to make the movie (I bet it's probably one of his favorites), but he's got to make his movie not QT's.
I also think most of the deleted scenes should be in the movie, like the Hun bros, Mickey in the courthouse,Dennis Leary. The length wouldn't have mattered to me.