Pros
Morgan Stanley is one of the most respected brands in the financial industry. It excels in a number of areas (top 20 places to work at) so having it on your resume is definitely an asset. The compensation package is good, and comparable to those at similar institutions. The corporate culture favors growth without aggressive competition between employees. I had a great time there. Interns have a lot of added activities; they visit the city, get taken to social events etc. Plus the city of New York is a really nice place to be.
Cons
You are expected to work a lot. Because much of your compensation is based on bonuses at the discretion of your manager and that everyone else works between 9 and 12 hours a day, you are expected to do the same if you want to succeed.