Depends on the class.
One 300-level class that I remember was Modern Hawai'ian and Polynesian Literature, or something like that. (It was the '90s at the height of the PC movement, so my school had a Race or Ethnicity requirement, and that class was the least offensive I could find that would still count toward my degree.)
Let me check…
…yeah, here's the guy. He moved from Michigan back to Washington State, but he seems to still be teaching essentially the same courses.
http://depts.washington.edu/aes/faculty/ssumida.htmlThat, plus a lot of Melville. It wasn't particularly hard, and he was much nicer than most professors at that level, but it was a LOT of reading. At the end of the term, he invited us to his house for a
luau.
I think the biggest difference you'll find is that 300 and 400-level classes are much smaller and more specialized, with more class participation and direct interaction with the professor, so you can't bullshit your way through like you might in a 100 or 200-level class with packed auditorium lectures and indifferent teaching assistants.
EDIT: Oops, I didn't realize the thread was so old.