What causes this ?

Im using a prusa i3 running on GT2560, Im unsure why im getting this finish however the dimensions are accurate.

Thanks in advance

at first glance id say over extruding and too cold.

When i get new filament i always print a test piece Normally a 20 X 20 square hollow that 100mm high as it prints and assuming PLA i start to 200 deg then reduce by 5 deg every 6 mm height ( sometimes mark the height where i change with a felt tipped pen)
If you model is hollow you could pretty much do the same to find the best temp for that filament
good luck