MathWorks' Support Response:
I have been able to reproduce the slow down that you were experiencing. The fsurf function tries to determine what density of points to use in order to give an accurate depiction of the function you pass it. Since the ackleyfcn has many small oscillations, fsurf decides to use a very dense mesh in order to display it. This feature is not available in ezsurf which is why the plots look so different.
The time fsurf takes is also much longer because if it displaying many more points. If you would like to use fsurf to produce the plot similar to ezplot, you can turn off the AdaptiveMeshDenstity feature by using the following line of code:
set(fsurf(@(x,y) ackleyfcn([x,y]),[-32 32 -32 32]),'AdaptiveMeshDensity',0,'MeshDensity',60)
Note that this will increase the speed of fsurf and will produce a plot similar to that of ezsurf. However, this new surface uses fewer points and so does not fully represent the ackleyfcn function.