Two things about him really bothered me:

1) Lectures are pretty incomprehensible. He writes messy, writes everywhere, and does not label things well. If you already understand what he is talking about, then this isn't a problem, but if you are like me and had no idea what superfluidity (or various other things) was, then you will be writing like mad only to later figure out that you have no idea what some equation or graph even meant.

2) He lectures on things that he never has any intent of testing/making you do a report on.

For 18L this was certainly bearable, as our TA was great and let us know what was expected of us (though was not the type to just hand out A's), though I cannot imagine how incomprehensible Rosenzweig might be in a regular lecture.