Roundabouts are great when there's one lane in either direction. They start to suck once there's more than one lane, since the inner lanes have to cross multiple lanes when entering & exiting the roundabout.

There is a diverging diamond interchange across I25 in Cheyenne, WY, and the next exit just a couple miles south is a double roundabout. It's almost like WYDOT is conducting intersection a/b testing.