Was the Kansas-Nebraska Act controversial?

Yes

Explanation:

The Kansas-Nebraska Act allowed each territory to decide the issue of slavery on the basis of popular sovereignty. The Missouri Compromise had prevented this from happening since 1820

yes very very very controversial. it allowed each territory to decide the issue of slavery on the basis of popular sovereignty. Kansas with slavery would violate the Missouri Compromise, which had kept the Union from falling apart for the last thirty-four years so basically it allowed slavery into the territory north of the 36'30'' latitude which had previously served as a boundary between the slave and free states.