I've recently left to retrain.
I would say crap pay compared to private sector equivalent jobs but very secure, loads of room for progression (in big cities anyway). Good union support. Flexible working although in some departments there is an unwritten competitiveness about staying in the office as much as possible, going to every meeting during the day to show face, then working until late. Don't get sucked into this, it is the most unproductive, performative nonsense there is.
Very bureaucratic and if your face doesn't fit it can be miserable as departments can be so set in their ways and culture (I'm thinking Whitehall). Clunky recruitment processes.
However, I had a really interesting career, got loads of experience, travelled, did language training, was treated well when I had to have time off sick (ongoing illness).
In the place where my face didn't fit, I just built my experience there into good conpetencies, dusted myself down, and moved on. There are always jobs available and it isn't looked upon unfavourably to move fairly regularly as long as there is some logic to your path- either moving up or getting relevant experience.
There's scope to move around the country and overseas (although overseas posts are being cut, certainly in the home office).
You'll come across plenty of examples of Peter's Principle due to the job security and opportunities for progression, meaning sometimes inept senior staff who would have been long gone in the private sector.
Overall a positive experience for me, if some way from perfect.