Definitely not the same, at least in my experience. It differs by field, but in my field, grad programs basically have zero classes, and whatever classes there are are generally automatic A's. In turn, the difficulty comes from the fact that you are basically in indentured servitude to your advisor, and there is no actual recourse for trivial things like "overwork" and "burnout."

I know of people who did 70 hour work weeks, and for a period of time, I had to do that as well. Also, you get paid less than you would if you had just gotten a 40 hour per week job at a company.

Anyways, the advisor that you pick really makes or breaks your experience.