For a first approach, ICEM is quite difficult to use especially because of the multitude of the options. For instance to do one action there more than one possibility:to create one point you can enter the coordinates, considerate as the intersection of two lines etc.... After that, the mesh part, concerning the "blocking", the different projections it is necessary to do is quite difficult to perform. So it is possible to prefere other mesher like Gambit or preBFC.
It is true for quite simple geometries, but in how many time do you think you can do that with preBFC ? :
Finally, concerning the mesh, there is a variety of options it is impossible to find in another mesher. It is possible with ICEMto define the mesh as we want.