Pros
As a software engineer, the work was interesting. My management looked to me for most of the technical direction of our product, which was satisfying. My requests for resources and purchases (e.g. laptops, books, commercial software utilities) were never denied.
Cons
During my 3.5 years at KLA-Tencor two of my managers were put on performance warnings and ultimately dismissed from the company. My last (third and final) manager was put on performance warning after 8 months, which is the reason I resigned and took a position elsewhere. I don't consider it professional to give the details of the aberrant behavior I witnessed from my managers. I will just say my experience was bizarre and unsettling. As an individual contributor, I only interacted with the lower levels of management (line-management up through mid-level management), so the more senior managers may not have the issues I witnessed. I am giving the KLA-Tencor's CEO (Rick Wallace) a low rating because all I can really judge him on is the culture he created that I worked in (described above) and the value of KLA-Tencor's stock during my time at the company. When I started the price of KLA-Tencor stock was $50/share, and on my last day it was $39/share.