Pros
Friendly and enjoyable working environment. Pretty good perks and benefits. Salaries, although often lacking transparency, are nonetheless generally good. The cafeteria is excellent and the whole organisation (at least in Fontainbleau) has a good vibe. It's a driven working environment, but that feels positive rather than overbearing, and it's a source of pride to be working for such a prestigious and globally respected school with incredible alumni.
Cons
Your pay is anchored by your starting salary - if you sell yourself short when you join, you may stay behind the curve for several years, irrespective of performance and promotions. Salary progression significantly rewards length of service over annual performance, despite assertions to the contrary. That's great if you're local and/or planning to work there for decades - less good if you expect to be equitably rewarded and/or promoted for your performance in a given year. This is also reflected in the culture of the organisation - new ideas can sometimes be met with suspicion. Non-French hires to managerial positions should also be aware that France's (excellent) worker protections can also hinder even the most innocuous decision-making, in some contexts. It's quite common not to be able to find budget for something business critical, at the same time that staff are needlessly shuttling between campuses using expensive and environmentally unfriendly means.