<p>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.</p>

<p>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.</p>

<p><a href="https://i.stack.imgur.com/MNLHp.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/MNLHp.jpg" alt="Left hand side of the print shows uneven and rough lines"></a> </p>

<p>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?</p>

In case of such difference in printing in different directions you can check if;
for x and partially z axis
filament is blocked and cannot be pulled as it should
spool is blocked
for x and y axis
rods on which caret/HB is sliding are parallel
timing belt idlers are parallel and they are in a line
Shape of the nozzle or its perpendicularity should not be the case as it's hot and it wipes layer itself.
You can also check if it's not an issue of cooling fan. It can vibrate as such.
Eventually it could be an issue of cooling itself. Let's assume you have cooling fan at the back and it pushes air to the front then when caret moves from the front to the back then cooling time is longer than when the fan goes in opposite direction.