Vantaggi
Microsoft values intelligence and initiative. If you have a good idea and are willing to work to make it happen, you can. I have worked at Microsoft for nearly 13 years and, while the "good old days" had some great things (more money, fewer layers of management) the company has gradually improved in most ways. People are more respectful of each other. The company is more diverse. There is a greater variety of jobs and opportunities to pursue. As a post-adolescent company, Microsoft increasingly values work/life balance. You are expected to work hard but don't need to kill yourself unless you really want to. The other thing that I think is cool about Microsoft is that the company generally doesn't give up. 15 years ago, Microsoft was a PC software company. Then management decided that Microsoft needed to be an enterprise software company too. Nobody gave Microsoft much of chance to be a serious enterprise software company. Today, most big companies use Microsoft software. Similarly, today most don't give Microsoft much of chance of being a successful "internet" company (vague definition, I know). But Microsoft will keep at it and will eventually succeed. No, we won't "kill" Google. That's not the point. But Microsoft and its employees are tenacious and that's a great quality for a company and its employees.
Svantaggi
The increased size obviously has downsides. I'm sure there are great ideas that die on the vine because the peron or group that developed the idea didn't have the ability to make it happen. That's unfortunate and could be improved with better management practices. Microsoft also can feel a bit impersonal. That's also partly a result of size and scale. But I think it's also partly due to a loss of some of the original zeal that employees had - the feeling that we were working to change the world. With more people you naturally get more dim bulbs and that has a negative result on the whole.