For the visuals: increased bloom, fog to max, different colors, caustics light emitters, colored fog, ..
maybe make it appear like underwater somewhat like so:
http://static-3.nexusmods.com/15/images/110/2762305-1384670704.jpg
or so
http://3.bp.blogspot.com/-gqMMmRXLG9U/URaFxv8RI1I/AAAAAAAACnw/uV8mYQMiXws/s1600/Nereocystis+luetkeana-+bullwhip+kelp03.jpg
or so
https://www.youtube.com/watch?v=3D9OTNhubbA
maybe different movement, different sounds, occasionally you having nightmares due to the zombie apocalypse or illness, maybe with additional zombie noices, twiggs cracking and heavy breathing (think of the Max Payne dream scenes), different perspectives, sometimes doom and gloom, other times sweet dreams and increased white bloom. the potential is huge!
just different everything. it is a dreamland after all ^^
and if you get shot in dreamland: "OMG! PHEW! PHEW! PHEW!! oh boy! thank god it was just a dream.. my stuff is still here." :) as you wake up sweaty next to a fireplace or in midst of a thunderstorm at night..
or you go to sleep and log out like that and when you log back in later you are well rested. so you don't have to go through nightmare mode if you don't want to.