Opera 12 keeps the general design and functionality of the highly-praised Opera 11, but adds convenient improved features like themes, web cam access and hardware acceleration. As for the the interface, Opera 12 features a slightly cleaner GUI with a focus on webpages instead of buttons and menus. Overall, Opera 12 isn't a huge change compared to the last version, but it has been improved with some nice new features.
The big innovation in the last version of Opera was extensions and while the choice of browser enhancements is still fairly limited, when you install or uninstall add-ons, you don't have to restart your browser. They are also sandboxed, so if one crashes, your browser won't. Opera 12 runs just as quickly as Google Chrome (the developer claims it's even faster) and the rendering engine has been tweaked slightly to offer an even faster browsing experience.
Visual Tabs and Tab Stacking is useful if you often have too many open, and there are now visual mouse gestures. These are well implemented, and accessed by holding the right mouse button which brings up a translucent guide to mouse gestures. This is a great introduction for people who've never used gestures, and hopefully allows for greater use in the future.
There's still an integrated mail client, which continues Opera's move towards doing everything you need in one application. The newest features or improvements of note are themes and web cam access. The most notable improvement has been to Speed Dial which instead of simply giving easy access to your favorite sites, now allows you to embed your Speed Dial with dynamic information - in other words, web apps within Opera. Meanwhile Password Syncing allows you to sync passwords across machines and devices - just sign-up for an account and Opera does the rest. There have also been some HTML5 improvements for developers such as Session History, Navigation and the W3C File API.
Conclusions
Opera 12 is a definite improvement on Opera 11 although the changes aren't revolutionary. However, if you're looking for a new browser, this is probably the most innovative currently on the market and is well worth installing.
Recent changes
General and User Interface
Fixed an issue where Opera gets internal communication errors on Facebook
Fixed an issue where no webpages load on startup, if Opera is disconnected from the Internet
Fixed an issue where images will not load after back navigation, when a site uses the HTML5 history API (deviantart.com)
Linux and Windows
A new stand-alone update-checker, as part of a planned upgrade of the auto-update system
Windows
Improved protection against hijacking of the default search, including a one-time reset
Security
Fixed an issue where DOM events manipulation might be used to execute arbitrary code, as reported by Arthur Gerkis; see our advisory
Fixed an issue where use of SVG clipPaths could allow execution of arbitrary code, as reported by anonymous via the iSIGHT Partners GVP Program; see our advisory
Fixed a low severity security issue; details will be disclosed at a later date
Fixed an issue where CORS requests could omit the preflight request, as reported by webpentest; see our advisory
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