The main problem is that the best people are leaving, and those who remain are less and less competent every year (but don't seem to know that). It seems that the best new hires don't want to work at Microsoft and choose to go elsewhere.
Recognition and career success comes primarily from telling management what it wants to hear, rather than from good work or doing what customers want. In the past, middle management was technically competent but mediocre at managing people (which they knew, but didn't care). Today, management is too often poor on all dimensions but doesn't even know it. Many managers are incapable of recognizing good work, much less knowing how to do it themselves or how to encourage people to deliver it. Managers take care of themselves and their peers first, suppressing other opinions, rather than standing up for employees.
The company is a giant bureaucracy. The easiest way to succeed at Microsoft, like any bureaucracy, is to tell everyone what they want to hear, keep your head down, and don't challenge anything. It's better to do work that is tolerably good but not excellent (because great work would be a threat to others). This attitude seems to come down from the top, where very real threats to the company are covered up in platitudes about how "next year will be great!", year after year after year.
Having said this, the culture varies from group to group; some are awful while others can be supportive and good places to work. However, it's impossible to know in advance what any group is like, and continual reorganizations (every six months on average) mean that it could change at any moment and go from great to terrible with no warning.
Another major problem is the review system. Employees are forced onto curves within their groups, regardless of the group's overall strength, and managers are able to pick and choose peer feedback to punish anyone they wish. If you happen to end with a manager who doesn't like you or feels threatened, then you will get a bad review. And only the most recent review counts for anything. Even with a string of great reviews, if the most recent one is bad, you will be unable to look for other jobs within the company. Thus, a single bad manager effectively can force you out of the company. This explains why employees worry so much more about telling managers what they want, rather than doing great work.
Given increasingly incompetent management, flat stock price, and disincentives for excellent work, it's no surprise that the best employees are leaving in droves for Amazon, Facebook, Zynga, startups, and pretty much anywhere they can. The primary barrier to the exodus is that there are not many options in Seattle.
In short, if you would like a nice office and benefits but don't care that much about your work or career path, OR if you prefer to play politics and don't mind backstabbing others, then Microsoft could be a good place for you. But if you want to excel, to do something interesting, or to be rewarded for real innovation, it's the wrong place.
