Vantaggi
If you're lucky and proposed a position in one of their middleware departments you might tackle with some interesting problems. If not, just don't take the job, it's not worth the cons.
Svantaggi
Unless you come from one of the top French engineering great school, you will always be seen as a second class player. As a consequence, lots of experienced developers get frustrated and leave the company after 2 or 3 years (contractor and staff alike) so that remaining engineers are very average, not really passionate with their jobs and only sticking with Amadeus to enjoy outdoors in the French riviera (9:30am-5:30pm + 2h break is not uncommon). The company isn't really agile and still struggling with legacy technologies (they claim they got rid of the legacy mainframe infrastructure but they didn't), so don't expect working on shinny bleeding edge technologies and be prepared to deal with boring stuff like TPF, TN3270 ... Senior employee (especially on the operation side) are unhelpful since they don't want to see their stuff decommissioned and have to work on new things. Dealing with employees (including management) who have no idea what they're doing isn't uncommon. On an average I spent 70% of my time doing maintenance work. Quality process is on a per team basis and almost in-existent.