Some are harder than others. I learned paper piecing by taking a class that used a pattern (Indian Summer) that Judy Niemeyer made for teaching. That one is very easy to make. Once you are comfortable with paper piecing, the patterns aren't hard to sew. I was surprised when even the curves went together easily, and I hadn't sewn curves before. The one caveat is that IMHO the instructions in the pattern are not well written, and I have found lots of mistakes in each one I've done. (I think the later patterns may have fewer mistakes than the earlier ones.) If you already know paper piecing, you will not be relying entirely on the instructions but will know what needs to be done, so it will be easier, but if you're trying to learn paper piecing from her more complicated patterns you may have problems.