Denver has a handful of growing roundabouts in newer neighborhoods, but unfortunately they keep installing them in all the wrong places. I'm convinced they are "testing the waters" by placing them in residential neighborhoods with very little traffic, which honestly just makes people annoyed by them, rather then appreciate them.
Roundabouts aren't a replacement for stop signs, they are a replacement for stop lights.
Some of the most egregious roundabouts I've ran (heh) into have been in Aspen. They're right after you get off 70 (ie going 65/70 mph) and are often overgrown with bushes and trees. I'm all for roundabouts, I think when done right they're great, but I don't know what they were thinking when putting these in.
I remember when they installed one out in Littleton (suburban Denver) - it flows traffic spectacularly but it took years, maybe even a decade for people to get used to it.
I once came upon it and found a full size four door sedan in the (raised) island in the middle with four befuddled teenagers standing around shaking their heads. They had plowed into the traffic circle straight ahead, jumped the raised embankment and landed right in the center island.
But the roundabout saved them. If they were not paying attention, as clearly they weren't, then they could have had a collision in the centre of an intersection. Better to end up in the he Center than t-boning a car.
Light traffic residential areas are a perfect place for them. There's nothing more annoying than observing a stop sign in an empty road. I have roundabout near me and when there is no traffic on the roundabout you just drive through it. The residential roundabouts have only a slightly raised centre so you can drive through in almost a straight line.
Late at night when there is no traffic it saves having to stop at all.
I think the exact opposite, that four-way stops should for the most part become roundabouts, and that's it. And actually, just four-way stops between two-lane roads, once you start adding lanes it gets too complicated.
In Spain, basically everything is a roundabout, so much so that when the roads are big enough they have lights within the roundabout. That's way too much IMO.
Roundabouts aren't a replacement for stop signs, they are a replacement for stop lights.