I have updated two different Piwik installations from 1.12 to 2.0.2 and after the upgrade I get this error:
Fatal error: Interface ‘Piwik\View\ViewInterface’ not found in /home/northern/public_html/piwik/core/View.php on line 110
The workaround is to press the back button and then click on “Go to Piwik”, so this is just an irritation 
Neil