Sweden's economy grew 4.5% last year and is expected to grow 3.5% this year. The central bank lending rate is -0.5%. (I believe that Sweden was the first to go negative.) The bank has also done the requisite quantitative easing. The fly in the ointment is that inflation is only 0.4% whilst the target is 2.0%.
Personally, I don't see why stable prices and a booming economy is not considered a good enough result. The Central bank, which seems quite pleased with itself, says, however, that it needs more power so that things will be even better.
It's human nature: everyone thinks he ought to have more power.