Well, every single year of medical school is actually equally difficult. I will even say that the last two years are more difficult because you are not as much in charge of your career as others are. There is a difference in how they are difficult. During first two years you study all the time and the work load is huge. During 3rd and 4th year you work really hard to set yourself up for residency. Although study time is reduced during 3rd and 4th year, dealing with politics, bad rotations, unfair evals, and the application process for residency more than make up. So don't be fooled when people tell you it gets better during 3rd and 4th year. It won't. It is different, but not at all any easier.