The feature I absolutely love on Opera mobile is it will dynamicly wrap text and adjust the page layout to a single column when you zoom in/out. So for pages with small text, you can zoom in to see enlarged text and just scroll down to read - where on all other browsers you have to scroll horizontally back and forth to read the enlarged text.

Opera has been doing this brilliantly for at least 10 years, and I have yet to see this on any other mobile browsers I've tried.