MS seems to have done rather well here. They paid considerably less for Nokia than Google did for Motorola. Good for them.
However, if they want to grow market share, they will need a more intuitive interface than Metro. Whether you like WP8 or not, at first glance it looks cluttered, inefficient, and confusing. You could argue that it's actually nice once you start using it, but having to repeatedly convince people to try it isn't going to grow your market too quickly. Maybe the Nokia staff previously working on other operating systems can help with that.