Pros
I get to work with intelligent and supportive teammates every day. Amazing facilities/gorgeous landscaped HQ. Work/life balance is very good for most SWE Interns I know. Free drinks They bring in good musicians to play over lunch at the main cafeteria. Performance feedback is not only focused on individual contribution, but also how well you work with others. I've been told this really improves the company culture, especially on the main campus. They make an honest effort to give interns projects that are interesting and within the scope of a summer. Top notch health insurance, even for interns.
Cons
The culture of different teams can vary (I have heard good and bad from other interns.) Microsoft always manages to stay in the news with the latest PR gaffe (honestly more amusing than upsetting to most employees.)