For the uninitiated, Jackson's EM book is considered the book on E&M. There really is no other book to learn from, if you want to learn EM correctly.
It is also horrifically difficult even for dedicated PhD students at top 50 physics programs.
Story time:
As an undergrad I had a TA that was in the astrophysics program. He told us a story of a final he had to take in his EM class, using Jackson, of course. The final was to present his solution, if any, to the PI. Pass or Fail. He went home and started work on the problem about three weeks before the due date. When his wife would go to work, he would be sitting at the kitchen table, when his wife came home, he was still at the table. For weeks straight. As the deadline got closer, he started sleeping less and working on the problem more. In the last few days, he stopped sleeping entirely. Eventually, he gave up on the problem and took the bus to campus to report on his failure and receive the Fail. Once his deprived mind relaxed on the bus, he had a Eureka moment and was able to solve the problem. Unfortunately, his sleep deprivation caused him to hallucinate. While presenting his hastily put together findings, he was trying to dodge imaginary bats, deal with imaginary blaring car horns, keep from falling asleep while standing, and present very nuanced and complex EM equations. After the presentation the PI said: "Pretty Okay", and passed him.
This is considered a slightly atypical end to a semester with Jackson.
How bad Jackson is depends highly on which problems are attempted and in which context. The content is fine and perfectly understandable. We used it during my third year of undergrad. Homework mostly consisted of the easy-to-medium problems, and self-study could focus on the medium-hard.
Between that and the highly-abstract statistical physics course (it started with an introduction to differential forms), I learned more in my third year of college than in any other.
It is also horrifically difficult even for dedicated PhD students at top 50 physics programs.
Story time:
As an undergrad I had a TA that was in the astrophysics program. He told us a story of a final he had to take in his EM class, using Jackson, of course. The final was to present his solution, if any, to the PI. Pass or Fail. He went home and started work on the problem about three weeks before the due date. When his wife would go to work, he would be sitting at the kitchen table, when his wife came home, he was still at the table. For weeks straight. As the deadline got closer, he started sleeping less and working on the problem more. In the last few days, he stopped sleeping entirely. Eventually, he gave up on the problem and took the bus to campus to report on his failure and receive the Fail. Once his deprived mind relaxed on the bus, he had a Eureka moment and was able to solve the problem. Unfortunately, his sleep deprivation caused him to hallucinate. While presenting his hastily put together findings, he was trying to dodge imaginary bats, deal with imaginary blaring car horns, keep from falling asleep while standing, and present very nuanced and complex EM equations. After the presentation the PI said: "Pretty Okay", and passed him.
This is considered a slightly atypical end to a semester with Jackson.