The free version display ad banners at the top of the window. To make them go away, you can buy a license at 34 EUR. If you happen to have issue 8 of the german c’t magazine, you are eligible to buy the browser for only 8 EUR – a great deal!
Oh, and here are the new features and changes: Opera changelog
I have been using Opera since version 7.x and never want to use any other browser. The most useful features in my eyes are: Tabbed browsing Support for sessions (opens a set of sites you browse regularly) Mouse gestures Quick Preferences (now, you can enable / disable you proxy with just 2 (!) keystrokes)