There are a few things I'd fix with MS, but I would definitely start with the forced curve system. It's basically evil.
Sort of balled-up in this is the sense of fear that forces people to make bad decisions just to get promoted (my favorite example of this: The "Metroization" of the Visual Studio 2012 interface, with nearly unusable color schemes and all-caps menus. I have to assume that somebody got promoted because making VS 2012 look like the flavor of the day looked good on a review).
I was in Xbox, which had a /lot/ of very, very good people in the same review band that I was in. It's hard to shine when you're sitting next to those folks; it's also hard to imagine not working with them, because one of the reasons I go to work is to study at the feet of masters.
So I was looking at an "okay" review, maybe even "sub-okay", while doing work that would probably have brought the company a few hundred million dollars over the next ten years. And I couldn't stand it. And that's one of the reasons I left.
Seriously, fuck the Microsoft review system. It's broken. Most everyone with a brain /knows/ that it costs MS really good people. But Ballmer and Brummel (the head of HR) seem to love it; maybe it makes it easy for them to remove threats? I honestly don't know why they think it's good.