My complaints about Opera have more often than not been about the UI. Even at this very early stage for this version, things are noticably improved, with better Windows 7 integration throughout including glass, jump lists and tab previews in the task bar.
On the CSS front, things are even more peachy with the addition of rounded borders (finally!!), box-shadow, transforms & transitions and multiple backgrounds. Suddenly my website actually looks like it's supposed to instead of something from a previous era. I can properly recommend Opera to web developers looking to make beautiful websites using the best of CSS available. There are a still a number of bugs with rendering but these could easily be ironed out by the time a release comes around.
And speaking of rendering, the new engine also brings "Vega" which uses GPU-accerleration to render the page. Both Firefox and IE9 have Direct2D acceleration in the works. Vega uses DX9 rendering, which, if I'm correct, means that Vega will also work for XP clients, where as Direct2D is sadly only a Windows Vista / 7 affair. This will win Opera some more fans.
Chrome has unquestionably really stepped up the level of competition in the browser market. Chrome has shown that speed has to be across the board, and that the 90's style UI layout is outdated. Yesterday, some new mockups of Firefox 4.0 were described and the direction is very clear. More like Chrome. One thing is interesting though, this new Opera comes with a button for the menu just like the Firefox mockups!
I actually think this is a wonderful thing, and I hope the idea is 'stolen' by as many people as possible. It works a lot like the application's menu in OS X. Anything pertaining to the application as a whole, and not just the in-page content should go in the application menu. This idea has appeared in a number of different styles in recent Windows apps but no consistent style has been agreed upon by vendors. Microsoft Office uses the office button, office 2010 uses a blue "File" button, MSPaint in Windows 7 uses a similar blue button, but with an icon, and Chrome uses the
wrench spanner button on the right. I toyed with the seperation of application level menus and document level menus in 2006.
To better help tab users Opera have moved dialogues in-page so that they are not modal to the application. This seems like a bad idea, as it's incredibly easy to spoof these dialogues and steal people's passwords in phising attacks. Google have managed to do a much better job with per-tab modal dialogues and Opera should copy this idea instead.
The biggest dissapointment? No HTML5 video. An experimental version of 9.6 was released with HTML5 video and we've seen nothing since. With three main browsers now supporting HTML5 video, this leaves IE and Opera. Both of whom are keeping shtum at the moment. Given that embedding plugins in Opera is far from snuff (No embed element support _at all_ for QuickTime on Windows) this is important to me--I don't have Flash installed and rely on HTML5 and various shims to watch video online.
Overall Opera 10.5 pre-alpha achieves one main thing -- it makes Opera a browser developers would actually want to test with and develop for. I could not have said that of previous versions. Whilst this is a pre-Alpha release, it shows a lot potential promise, and I would actually encourage web developers to download it right away and start testing their site against the new CSS capabilities.