I'm doing a masters in English at the moment. My experience is that the amount of work fluctuates, but at its peaks it's more intense than a normal job (I exclude things like being a firefighter or working in a bootstrapped tech startup).
This spring I had two 7k-word essay deadlines and a palaeography exam within a fortnight of each other. That was substantially more daily work, for at least a month and a half, than a full time job, or at least than either of the full time jobs I've ever held down. I had three proper holiday-style time-with-your-family days off at Easter, after flying home on Good Friday from a field trip.
It's also work that tends to stick in your mind even when you're not working, unless you're better than I am at compartmentalising these things. Some jobs you can go home at the end of the day and just forget about work until you get to your desk the next morning; my experience with this course has been that it takes over your mind, and it takes over your home too (notes and books everywhere).
's good fun, though.