He has knowledge of software and that's one of the main areas where Nokia has to develop. He worked only 2.5 years in Microsoft so it doesn't matter that much.
Finnish media has been saying that he was a safe choice though they are saying that Nokia should have made more radical move. One of the biggest issues is that people don't want to work in Finland as here even big bosses don't get paid as well as they get in US for example. In 2008, Kallasvuo got "only" 1.2 million Euros as salary (total incomes were 8 million according to tax office). Another big issue is that Nokia's board of directors contains mainly Finns and that may not be that attractive for foreigns, especially as the CEO has always been a Finn before.
I'm not making any conclusions yet, everyone deserves a chance.