Civil Service, small department here (and not a particularly controversial one either!)
Perks:
We are a homeworking first dept, the flexibility in this is the best I have ever had in my working life. (Its a department that wins a lot of flexible working awards in parenting groups/circles).
Pension: I think its exceptional, seems to be consensus its a good one in my family.
Development: I know this is personal to each person and department, but I have had amazing support in development in my career - all my managers have been great in this dept, and have given me budget for qualifications I could use elsewhere, private and public sector.
Cons:
Pay. I think at the lower levels, pay is good, in my area at least (i live in a town where incomes are low), as it creeps up the grades pay is not competitive with private sector and constantly subjected to pay freezes. Little room for negotiation at lower/mid levels.
Institutionalisation: Lots of folks who are lifer civil servants and stuck in their ways. Not so many where I am now, but they are in every department in my experience.
Slow moving: getting anything done at pace is a nightmare and sometimes frustrating.