The only problem with courses like calc 3 and differential equations (in my experience, as a mathematician) is that they are cheating somewhat. By cheating I mean relying on inadequate, flawed or entirely omitted proofs. How can the students truly understand something if they are not presented the whole story (or at least reference)?
The good thing about these courses are that there are usually no shortage of relevant exercises!
I detested differential equations. However, that was more due to how it was presented than the underlying, surprisingly, beautiful math.