Having traveled in Mexico quite a bit before and after NAFTA, I can tell you NAFTA has definitely succeeded in creating a more prosperous middle class there, especially in the larger cities, and this in turn has actually boosted US exports to Mexico, where trade used to be mostly the other direction.
However, other NAFTA policies weren't such a great benefit, in part because they were incomplete and skewed toward American interests. For example:
- Separate rules for maquiladoras left them unregulated and a source of significant labor exploitation that contributes to border instability.
- US agriculture subsidies, particularly billions subsidizing corn and soy, have virtually depopulated hundreds of Mexican farming communities, forcing millions of young men either to move to the United States to find work, or for farmers to shift to marijuana or other illicit crops to survive.
- Finally, but perhaps most importantly, NAFTA liberalized markets for (some) goods while failing to liberalize labor markets, which was a recipe for disaster. Markets don't respect national boundaries, so it behooves nations to create multinational structures to control them - that's especially true for the labor market.