Opera is my main browser. When a webpage doesn’t work, I just use Internet Explorer, but this rarely happens (damn online banking ¬.¬).
It does seem to take up a lot of RAM, but I looked this up and apparently it will happily release it if it is not needed. I’ve found this to be true almost all the time, but did get the occasional hang ups when I only had 2GB RAM installed (had to kill the Opera task). With 4GB RAM I’ve never had this problem, but that’s probably because of the spare RAM. Most computers come with 4GB RAM anyway, so it shouldn’t matter.
The extensions and widgets for Opera are mostly useful; not much rubbish, though aren’t that many. That said, many of features other browsers require extensions for are built into Opera (though can still be turned off). Mouse gestures, voice commands, bookmark syncing (Opera link - also covers mobiles) are all included. Opera Unite is very good (easy VPN, note sharing etc.) and of course there is the Speed Dial.
Sure, some extensions are missing (Zotero cough, though referencing isn’t that hard anyway ¬.¬), it can be unstable and some sites don’t work properly with it, but overall Opera is a great browser. Sorry for the wall of text.