I have been an Opera fan for a long time. The latest release, Opera 15.x seems a bit of a mixed bag for me. I agree about the "showing its age" for 12.16.
It always had a number of points of difference from the others (Firefox, Chrome, IE). But Opera 15 feels like Chromium with a new theme. I guess it's because of WebKit. But the configuration pages are almost identical to Chrome. Not that this is a bad thing, really - their reason was that they would contribute to make WebKit better, which makes business sense. But it's a bit of a "if you can't beat them, join them". I really resent the lack of ability to change the default search provider in the URL bar. I use DuckDuckGo and although I can add it as a provider, I am still limited to the usual "big 3" or 4 providers as default. Why, Opera? Chrome has this ability?
Now, regarding Mail, etc. I am using the independent new Opera Mail client and love it. It's in my opinion, way better than Thunderbird in the UI - very clean and refined and a evolution of the previous Opera Mail (integrated into the browser). Seems not much development is going on with it though, there haven't been any new releases since it was first released. And it's not that heavily marketed...
The thing I liked about the "old" Opera was it's difference from the other browsers. It's a bit of a Norwegian quirkyness, with some awesome innovations thrown in. And it worked well. I loved how it was different. But it seems more watered down and vanilla now, just another browser. Why use it? Not much reason now, might as well use Chrome and have better plugins. Or rekonq or arora, etc. All WebKit browsers.
Totally agree with being jibbed regarding Linux support too. So I use Chromium. Half because the Firefox UI is a bit ugly in KDE.