We used to have a plain stop sign intersection at the end of our road, which teed into a more heavily travelled road. It would sometimes back up 20 cars deep because someone was trying to make a left and just couldn't get a break. They have since replaced it with a roundabout and traffic never backs up and I can't remember the last time I even had to come to a full stop before entering.my biggest problem is the folks who completely ignore the 15mph signs and barrel through at 35-40! But even with such dolts the roundabout is better since accidents are prone to be glancing blows instead of right angle impacts.
The best multi-lane roundabouts I've seen are at Hilton Head, they keep the right turn traffic completely isolated:
