According to the announcement on the official website, the new rendering engine is 40% faster, the speed dial has been improved, the design was changed compared to 9.64, there is now a resizable search field, and a new browsing mode for slow connections, called Opera Turbo.
The first thing that jumped in my eyes was the new interface, Opera 10 beta using a blue theme, different from the black one used in 9.6x. Here's how it looks:
Opera allows now for tabs to be resized, and previews of the web pages loaded in them are shown in the tab space. Here's a screenshot to make this clearer:
Presto, the rendering engine used by Opera, has also been improved, and if we take into account what the official website says, it should be up to 40% faster compared to older versions. The Acid3 score for Opera 10 was maximum, 100/100, while Firefox 3.0 got 72/100 and Google Chrome unstable for Linux got 99/100.
Opera Acid3 Test - 100/100
The location bar (also called search field) can also be resized, leaving more space to the fast search box to the right.
Opera 10 has support for widgets too, just like older versions. Here's a crossword game, running inside Opera:
Crossroad widget running in Opera
As always, Opera provides packages for various Linux distributions, including Debian, Ubuntu, Fedora, SuSE or Mandriva.
Opera 10 beta comes with all the additional features its users are already used with: integrated BitTorrent, IRC and email clients, support for widgets, a sidebar which provides access to stuff like bookmarks or even notes. On top of this, Opera is highly configurable, allowing you to configure each and every aspect of it, from keyboard shortcuts to the user agent. Just like Firefox, it comes with an about:config configuration utility.
Opera 10 already looks very promising, and it's just in beta phase. Though closed-source, it always managed to keep its marketshare throughout the years, it provides very good Linux support (really, I don't know many - even open-source - projects who provide installation packages for so many distributions), it comes with Flash by default, and it's very fast at rendering web pages.