I have a Prusa i3 that I am mostly happy with. However, I am seeing these strange artifacts when the extruder moves along one axis in one direction - in particular from the back of the printer towards the front. The extruded lines look uneven and the surface is quite rough, but only in that area and only while the extruder moves in that direction.
Here is a recent print that shows this happen. The pieces were printed side by side, and both of them show this on the left hand side, while the right is okay.
I am thinking maybe the extruder tip is slanted (not perpendicular to the bed), which causes some sort of scraping while extruding? What do you think?