Pros
Top class IT infrastructure. Very aggressive work environment. People focus on getting things done. Multicultural workplace. If in technology, any system you work on will likely be handling a lot of money and that brings responsibility. Good exit opportunities. Not so good for lateral hires in tech, but takes care of its college hires (called NAPAs). Recommended for a 2-3 year stint only. You learn a lot, atleast in the beginning.
Cons
Work life balance goes for a toss, unless you are a team lead. The best work does not always come to India. Weekend support to ruin your weekend. The firm has too many local managers who are just not required, since work allocation is mostly done in NY. At GS, it's every man for himself and one can easily be thrown under the bus if not careful. Most people are high on IQ, but low on EQ. Salary is not so good to just ok, and it gets worse if you account for the long hours you will spend in office. Bonus is highly variable, don't count on it. Try to avoid work on their proprietary language (Slang). Visibility is a must for promotions, unless you are willing to wait forever. Underlevels employees when they join.