Dr. Kohen isn't the clearest professor I've ever had, but he's definitely the most intellectually rigorous. I took his British Imperial Literature class a couple semesters ago, and he's overseen my independent research this year.
In class, he asks hard questions so you better have done the reading. His was the only humanities course I've ever taken for which I had to reread my notes after class to really understand what he was saying, but at some point it all comes together, and he's really helpful for the final paper. Don't be afraid to approach him.
Unfortunately, he's going back across the pond in the fall, but take a class with him if he visits again. I'm applying to a PhD program at Oxford just so I can study under him...he's that good.
A word to the wise: he's a convinced deconstructionist, so watch out. One kid said something snide about Derrida and never heard the end of it.