New House, Horribly Patched Drywall
Perhaps the previous owners wanted the feel of some personality, or perhaps they shared their personality with the walls.

Since the house is new (to you) and you imply it  is yours and you want it to look good - plan to remodel it.

What do I mean? I mean, at the very least, plan to do new sheets of drywall where damage like that exists. It is pretty bad for the one picture you show and the time it will take to "patch in 4 sides" of a new rectangle of size 1'x 2' (just making that number up) may not be much worse in the long run of doing a 4'x 8'.

Not to mention, if you have any incling to change anything, run new wires (AC, HDMI, CAT6??), plumbing, or inspect the insulation, this would be a good starting point.

Getting intimate with the new place and fixing an eye sore.