Vantaggi
I had not worked for a very big company for ages, being in start-ups since 2003. My first reaction was not positive but I must admit that I was wrong. The company is a big vessel so do not try change its direction by yourself. Swim with the stream and make sure you work for an organization that is part of the overall strategy. I work for the Cloud and I must admit that we have nearly unlimited means to make it happen. You can propose ideas, it can take time and effort to get them adopted but that is part of the collaborative game. All the policies are written and they usually make sense and give you a good balance between efficiency and comfort. A lot of self service which can be a bit depressing at the beginning but once you have tamed the beast and know where to find the info you are your own Boss (or close)
Svantaggi
That is a big company so everything takes time. But as said before, if you swim in the right stream you swim faster than the competition. Can be frustrating to get decisions made as non critical ones make ages to go through. If you are in a business that neither a cash cow or nor on the strategic roadmap try to jump to another business rather thinking that you will be the last one standing. There is obviously a bureaucratic aspect that can see very heavy although once you know how to handle these process your life is fantastic. Don't try to be to creative unless you are in product as this company is so risk adverse that we prefer to turn down business rather than take a chance.