Very hard work.
It took me 20 hrs/week of study to earn an A in E&M. I had to review completely all the math before hand, mostly the relevant vector calc. which was nicely covered in the text.
My favorite part was the transmission line chapters, which fortunately in the course I took, was heavily emphasized. I learned a great deal. Doing all the homework, and not just to get the answers, but exploring tangential questions which arise, was also essential in driving it home.
I wish the course had the time to get deeper into the propagation of waves through various media & boundaries, since that topic is basically the physics of optics, which is also heavily involved in my work with lasers.
If I had had to take this course along with several others in a full-time curriculum, I may have not been able to study it to the depth that I did. Rather, I took it as a one-off paid by my employer.
Of course, I forget most of it anyway, but the course together with considerable time scoping at the bench with fast logic gates driving coax cables did give me a decent understanding of signal propagation enough to fix most cabling problems caused by clueless scientists, and to design decent PCBs and cable drivers.
I could pick up the more rigorous stuff like bounce diagrams and Smith Charts in a few hours of review if I actually needed to do these things again.
E&M is extremely valuable subject to master at the introductory level at least once, so that the insights into proper physics can guide your reasoning throughout the rest of your career--assuming you do some sort of electrical engineering.
Good day!