Pros
Free food, good work-life balance. Regular office parties, lots of free booze :). Firm seems to spend money like crazy, at the slightest excuse. Pity that they dont cut down on unncessary parties and so on, and increase employee pay a bit more. Work culture is good, and mostly your superiors are really open and accessible to you, no matter how low down the rung you are.
Cons
Difficult to grow as its such a huge organization. Not much learning happens, unless you spend a lot of time at the firm and proactively try to learn stuff. Job as such wont teach you much. Sad to say this, but the image of this company is overhyped outside. Most of the time you are actually doing backend, boring and monotomous jobs (with the possible exception of some of the sales guys).