Uranus’ moons are kind of unusual. They rotate (with the planet itself) about 90 degrees out of phase from the rest of the Solar System.
The usual nebular hypotheses for planet & moon formation come up dry when faced with this little factlet.
Saturn and a few other planets do this kind of thing, too — to a lesser extent — and also provide “little” puzzles for nebular theorists.
Neptune’s moons are just nuts — one (Triton) runs backwards and is in a decaying orbit; another (Nereid) is orbiting so loosely that it constantly risks escape.
These guys want new planetary formation theories, based around the widely-observed plasma effects. I’d be interested in seeing how it turns out.