Oxford doesn't offer the LLM. It does the Bachelor of Civil Law degree.
It is the premier postgrad law degree, perhaps, in the common law world. It makes the person vastly more employable, and more likely to succeed at the bar (solicitors do not take the degree as often). However, this is a law degree and a particularly sought-after one at that; it is therefore not comparable to an MSt in English Literature or the Classics.