I like how it responds so fast and works very well with Windows 7 64 bit O/S.
You also need the latest computer system with a CPU that runs 64 bit programs.
And you must have the proper amount of RAM installed in order to access 64 bit programs or it will be reduced to a 32 bit level.
I did not install the Flash Player at first, and when I went to You Tube to watch a video, the HTML5 kicked in instantly and played the video fine without glitches or audio problems even Full Screen.
So you need the latest PC system to take advantage of HTML5 working correctly.It runs full screen too, no glitches or audio echo.
Even with Microsoft's Silverlight plug-in in Opera 12 it works better than Flash IMO.
I have since installed Flash 11.3 64 bit version for Opera 12 mainly to watch videos on other sites that still do not use HTML5 (like ESPN) and it works well with the browser.
Also a CPU with 4 Cores is a big improvement to processing software rather than "old technology" of Dual core or Single core which really don't have the processing resources or fast enough chip speed to handle HTML5.
Opera 12 - 64 bit is very good...