There are 2 kinds of layout - one is full custom layout, usually for analog designs; the other one is standard cell layout, the layout for digital design. Both are equally challenging, in different way. Full custom layout engineer needs good knowledge of the process, circuit design and various layout techniques (like matching, noise isolation, etc). Digital layout engineer faces the challenge of ever-increasing size of the design (>10 million-gate designs are common these days). Full custom layout relies more on person's experience, and for digital layout, while engineer's experience is important, it is also heavily depending on the layout tools.