Pros
The work that you'll find at Sandia is unique in the sense that it usually falls into one or more of several categories: cutting edge research, national security projects, energy-related, and computing research. One could spend a whole career at Sandia, rotating about in various positions and departments, and acquiring new skills and knowledge all the while. For those people who want to work somewhere that is doing meaningful, important work instead of cranking away in a short-sighted, profit-driven corporate environment, Sandia is an ideal place to be.
Cons
Sometimes great work requires great sacrifice; travel is not unusual, long hours (as any engineering job will require) will crop up from time to time, and having to learn something new in a short period is the norm. Overtime is provided for Techs, and flex time (1 for 1) is given for Staff. Work hard, play hard, right?