Pros
SG is a galaxy, the possibilities for mobility and evolution are endless. The group accepts (tolerates) failure and average performance to such an extent and that makes it very human, meaning that a good balance will be found between your personal situation and your work. Lots of possibilities for overseas trainings and missions, hence this has been slowing down do the economic situation. Good work life balance, great benefits (holidays, pension plan...) A world-class training program and visibility to top management is fairly good for a group of that size.
Cons
Can be very bureaucratic and political. The double geographical and functional organization often leads to multiple bosses who often play against each other. The management style is post French WW2 style and did not much evolve since the 1950's: a French white man who graduated from X/Mines will be promoted better and quicker (unrelated to his performance). Salaries are disconnected from the market value and it leads to lose a part of the immense human capital available in the group. It is not rare to be proposed 30+% more outside of the group. The locations might be a challenge for engineers (industrial countryside areas).