I would say the first semester is the hardest. You are learning from scratch how to "think like a nurse," how to take the tests, and honing your critical thinking skills. For me, after the first semester, the rest is kind of falling into place and making more sense. The terminology is no longer foreign, I know how to study, and I know what to expect in clinicals. Also, once you get past the basics, the material is just plain more interesting. You're not dealing with basic nursing tasks, rather you learn about more specific disorders and interventions.
It also has to do with what other classes you are taking at the same time. For me, I took fundamentals, a&p and medical terminology
during the first semester, and now I'm just in nursing classes without other stuff to worry about.