At first you had to pay for it, then it was annoying adware. Sure, it was a snappy browser and I even used it for a while, mouse gestures etc. But there were always good enough free browsers available.

When they removed the ads in 2005 it was far too late, Firefox had changed the game.

And Opera is still not open source. Which makes at least a difference for some people.

Opera is amazingly fast too. Like Chrome/FF13. And smaller memory footprint. Its not marketed well unfortunately.