It was tragic when they they switched from the Presto engine. I was an Opera user from the exact day they stopped charging for it, but they slowly stopped innovating in ways I found useful and when they ditched their engine I ditched them, reluctantly.
Their big business idea was embedding and customization; the Wii's browser was an Opera derivative, for example.
I suspect they were an inadvertent victim of the smartphone/cheap data revolution. Products like Opera Mini (was that the one that did a lot of the lifting server side) were rapidly obsolesced when we moved from spotty data and Blackberry scroll-wheels to touchscreens and 3G/4G