It depends on where the roundabouts are used. In areas of heavy congestion they do need to be part of an overall plan of traffic flow.

OTOH I've driven in the US (about 3k miles around California last November) and outside of the cities traffic is light enough for roundabouts. I also think (but I'm not a road designer) that your typical street layout ought to be ideal for roundabouts as there are usually several ways you can get to a destination by just taking a later or earlier street.

In the UK we do also use traffic lights so I'm not suggesting replacing all junctions. It just seemed silly that several times I had to stop at red lights when there was no traffic. Worse still is the multi-way stop. Those could (IMO) all be replaced by roundabouts.

But, hey, I'm not a road designer - was just a thought