Where do I start?
It's fast, efficient, all-in-one (no need for plug-ins for almost anything I want, though I added one for zooming pics), a page zoom function, has had tabbed browsing for ages (first to do it?), mouse gestures (also first to have this? One of the best things ever invented), has integrated email client (I can't imagine not having this), very customisable, small file size, quick loading, no memory leaks, pop-up blocker been built-in for ages, content blocker (no ads on RG site, for example), tabs stay open when you re-load Opera, middle click scrolling is smooth (unlike others I've used), password manager, integrated "find on page", secure and safe to use (more-so than IE by a long shot), the most standards compliant browser AFAIK, site specific preferences, thumbnail previews on tabs, notes area (very useful), nice transfers manager, excellent searches for email/bookmarks/notes/contacts/etc, fast forward, full screen mode, the re-open closed tabs drop-down, fills in key words in input boxes (for example I can enter my name & address in boxes by pressing p, 2, n, m, c, t - the first letters of each part, and selecting them from a drop-down list - this is extremely quick) and probably loads more that I can't think of right now.
It has lots of other things I've never seen on other browsers, but those are the ones I use regularly.
Overall I think it absolutely fantastic, and probably my favourite piece of software I have on my PC. I've used it for about 6 years, and in that time it's been miles ahead of the competition in my view. Others have copied things from it, so people might not see as many advantages now, but I still think it's much better than any other I've used in the past (including the latest IE, and an unknown version of Firefox I tried a few months ago, that took forever to load).
I couldn't live without most of the features it has. Of course, with it in it's default settings I don't like a few things, so I'd have to change it to my liking - mainly moving the "bookmark/mail/contacts/history/transfers/notes" buttons to where I like them - see top left under "unread", the "Mail" section is displayed below:
This side bar pops out/hides with a click at the left edge of the screen.
Well, you did ask