So I finally watched this tonight and I get the extreme viewpoints now.
This movie is like being dropped into the most tense moments of The Wire without having any introduction to the characters or the plot. This leads to dialog and acting that feel incredibly awkward the first time you watch it. The whole movie just felt... wrong... up until half-way through the first scene in Cuba. By that time I had finally adjusted to the style.
It's a very off-putting movie at first brush and I totally get why a lot of people hate it. I ended up liking it in the end and I think I could end up liking it a whole lot upon subsequent viewings.
Mann definitely experimented with this movie. Filming everything in video at a video frame rate sometimes made it feel like a home movie or an episode of Cops instead of a Hollywood movie. This was an attempt to make the movie feel more real but sometimes it just made it feel amateurish, even though the image was in high definition and filmed by professionals. While it was an admirable attempt, it led to an effect somewhat like what's described as the Uncanny Valley in computer graphics. When it feels so real in one moment, when the illusion is broken, it breaks hard.
What I'm saying is that the style in which this movie was filmed made suspension of disbelief very difficult just because it's so different from anything else out there right now. And the way the movie opened didn't help any, as everyone seemed incredibly tense and depressed through at least the first forty minutes and because the characters were never introduced properly it was almost impossible to connect with them until half-way through the movie.
On the technical side, the video was just flat-out spectacular and the sound was great as well. To those who complained about the sound of the gunfire in this movie: You are wrong. You're too used to the cooked sound effects in Hollywood action movies. These were the sounds that the guns actually make and especially in that final confrontation, that's the way a firefight actually sounds.
Overall, I'd say that Miami Vice is a flawed experiment that grows on you. It's a good movie - after you've already seen it once and you've connected with the characters.