You could do a textured coating over everything to camophlage (I cant
spellll) the whole thing. A venetian plaster or a stucco type would
work well. If you want smooth walls, like one person said redrywall,
1/4" or mud the bad areas, and then hang a wallpaper liner paper, seal
that with an oil base primer and where the seams show mud those and you
are ready to paint, looks like new drywall only not retrimming out of
all your moldings.

Mickey