First and foremost would be the break in period. This is not a deal breaker, but this is something the runner does not have to go through considering the price. Ideally, this shoe should be ready to go once pulled outside of the box. However, once the breaking in is done, it should really be worth the effort.
Another less than ideal factor is the fragile underfoot nubs. While the shoe has really, really good grip, it would be worrisome to lose that grip once the soft nubs deteriorate. These nubs have been placed to less than 30 miles and significant wear is clearly visible already. Once the underfoot becomes more flat the normal outsole wear should happen.
The Primeknit upper experience is also weakened by the addition of the very stiff midfoot cage. Pure shape-forming feature is somewhat impeded by this plastic cage in the midfoot. Instead of trusting the elastic, but sturdy upper Primeknit construction to secure the midfoot, Adidas gave the job to the synthetic cage.
Other than these drawbacks, Adidas has successfully backed its claim of a cushioned and responsive ride that is excellent for long mileage runs.