Avantages
If you are in R&D, you will enjoy incredible job security. Nobody ever gets fired. You can go home at the end of the day and leave work at work. You can get by for years without ever doing any work. If you have a small startup, this is a great incubator. Just show up to work every day, appear to be busy, and they give you a quiet office, great healthcare, and will leave you alone for days at a time.
Inconvénients
You will work on some really unsexy products here, which tend to make it to market about 10 years too late (for example, their core product still has no way to make native REST calls and parse JSON endpoints). Build system is something out of the 90s. Hilariously lacking automated testing; a lot of it is done by hand, or by systems so brittle that they're only run manually. Simple bugs take months to fix. When I left, lots of development was still happening in Adobe Flash. Because of the high rate of tenure here, there is very little room to advance into management. Promotions are granted based on seniority. You can never make a difference here, and any disruptive ideas are squashed pretty quickly. Annual raises are percentage based; the only way you will ever see your salary increase substantially is by switching departments.