Pros
Above market pay for the hours and the work in my group was genuinely interesting. Not a bad place to work if you want a solid 9-5 and you're more interested in life outside of work than rapid career progression. My understanding is there are large variances between groups. In my group the managers and people were nice, intelligent, and truly did care but were also bound by the limits of the overall corporate structure.
Cons
I was in a young group, but outside of my group the average age is a few years shy of a retirement home. Especially with budget cuts, opportunities to truly advance are limited and lengthy with length of service being #1 over merit. Potential to get pigeonholed on multi-year projects building skills that wouldn't be useful outside of a utility. Moves at a governmental pace.