Tolkien's scholarship is always pretty impressive, even if it's out of date, now. Reading the bits of his lectures pieced together by his son is very interesting, and I rather wish I could attend them. (If I could be a member of Connie Willis' time travelling department of historians, I'd go visit Tolkien if I could.)

It's also amazing how much work he did on keeping the metre and language of Old Norse in a modern English version of the stories. The verse itself is probably the main attraction for readers. The story can be difficult to follow, but I think once you get into the swing of it -- or if you know the basic ideas already -- it's no harder to follow than a translation of The Saga of the Volsungs, though it is obviously in verse whereas that is mostly prose.