My colleague Marc Anderson, the "Knowledge Management Zealot," wrote a post "Getting Up and Running with Power BI and SharePoint Lists". The article intrigued me, since I have been following BI tools for a while and have used both Spotfire and Tableau in production settings.
Both Spotfire and Tableau are expensive and as usual Microsoft is trying to make inroads with Power BI. Tableau is my favorite. It is a well thought out tool, the application behaves crisply, and there are a large number of resources available to help you narrow down and get done what you need to get done.
In contrast to Tableau, Power BI still feels like it is in Beta, even though it has been out for a long time. Microsoft is making progress on this front and I believe they will catch up to Spotfire and Tableau. I am waiting for tight and seamless integration with Office 365. Currently it is tricky to use SharePoint Online as a source of data for Power BI. It is also not possible to publish a Power BI dashboard that contains sensitive data and have it shown in SharePoint Online. Hopefully this will be coming soon.