In my experience, lucid dreaming is as vivid and (un)realistic as any other dream, most of the time...except for the rare WILDs (wake-induced lucid dreams) where I fell into REM sleep rapidly and remember having fallen asleep. Those are often a bit less vivid and stable than other lucid dreams.

And flying is awesome! It's almost like there's no gravity, but not quite because you don't get nauseous. Gravity works well enough to keep your internal organs and sense of balance happy but does not force you to stay on the ground.