Some Janapese modern horror movies are very good. Strong plot, scary moments, good acting, while others are just.... unfortunately, Uzumaki belongs to the latter camp.
I will rate the movie based on 3 elements: Plot, Scary Factor, and Acting.
1) Plot - true to the name the movie, the plot moves in circle and never really explains itself. OK, the town is captivated by the spiral curse, but why? And why do people act so foolishly? There is a fleeting attempt to explain about what is happening by the reporter.. unforutunately...
2) Scary Factor - if this was meant to be a horror flick, it has failed miserably. I can't really remember one good scary scene with plenty of build-up to it.
3) Acting - very monotonous. People walking around, saying meaningless phases. I can't really feel much empathy for our tragic heroes.
All in all, there are much better modern Japanese horror movies out there with coherent plot and strong characterization. Don't bother wasting your time on this wannabe.