I had a 3802 and now have a 3806, which is a 3805 with a few extra knobs on and some light tweaking under the hood.
It would honestly be easier to list what isn't different. But sticking to sound, much clearer and more detailed, much more grip and ability to drive awkward loads louder and dynamics in a different class.
Downside - it's more complicated, which wouldn't be a problem but Denon wrote the handbook.
Russell