In short, resonators
- are louder than a wooden ukulele, and have more sustain than a banjo ukulele.
- have a more metally clang - depending on which system, brand, cone,... it's an acquired taste.
- have a bit of a different string physics thing going on, with strings pressing down on the saddle rather than pulling it up - hence players often use a slightly different wrist angle and often fingerpicks.
- have more factors that can be set up, or can go wrong - saddle height, buzzing cone... never change strings all at once, but one by one, unless you know how to set up without bending the cone.
- absolutely have a wide quality range, from cheap with a cheap sound to expensive with an expensive sound - you can hear the price difference!
- have different systems, aside from brands, which determine the sound: metal or wooden bodies, biscuit or spider cones, brass, steel, fiberglass or 'german silver' bodies.
I've had a gold coloured, steel Chinese one (don't remember the brand, alas), a Beltona fiberglass one, and still have a Dobro/Regal made Montgomery Ward one. They'r every nice, but I do seem to return to wooden ones after a while.