I live in the PNW. I like roundabouts where they fit, but near our house there's a super-busy one with multiple lanes that is just an accident magnet. People are constantly cutting across lanes while entering and exiting and sideswiping each other. It was originally a 4-way traffic light and it should have stayed that way. OTOH, we have a 4-way stop sign that is also an accident magnet during rush hour (when there's so much traffic that right-of-way is often unclear) and it should be a roundabout instead. Other than accidents from cutting across lanes during turns, the main failure mode I see in roundabouts is that they're subject to starvation while stop lights or stop signs aren't: if traffic coming one way never stops, then traffic to its right may never have a chance to go. I see this dealt with informally by folks voluntarily yielding but it's far from ideal (and unsafe because it's making an ad-hoc exception to a rule).