Opera has a lot of builtin features by default which are found only as plugins in other browsers. Some of these features include: email, BitTorrent, RSS and IRC clients.

Opera scores highly on HTML5 feature support. It usually shares the top place with Google's Chrome.

Opera has a functionality called Turbo which increases browsers speed and reduces data consumption considerably by compressing the data that's found in a web page.

Since Opera is built on WebKit, the same engine Chrome (among other browsers) is built on, it was possible for Opera developers to allow Chrome extensions to run in their browser.

A free virtual private network VPN is right integrated into the browser, keeping your browsing private.

Adblocker helps sites to load a little faster as lesser items are loaded (e.g. ads).

Opera is full of user controlled settings. Everything can be imported and exported even RSS feeds or emails. It can be skinned in a variety of different themes or it can be extended through the use of a large number of plugins available.