I talked to a lot of my peers about this and most say that medical school is much more time consuming. I guess it depends on your undergraduate school and your extracurricular activities, but I thought that my undergrad experience was busier.
In undergrad I was working weekends in a grocery store and I felt that I couldn't afford anything but an A in all of my classes to get into medical school.
Now in medical school I no longer work weekends and honestly I'm not so concerned if I don't honor (that's like getting an A) in every class (even though I probably should be). Of course that's changed now that I've gotten to third year, but even in third year, unless you're on surgery, it's a lot like working a full time job, in other words, not that bad. That's my opinion.
Of course in medical school you have to study a lot more etc etc... but you don't have to go to class either, so I think it evens out, furthermore I think some people's undergraduate classes were easier than mine, because there's no way I could have simply shown up and gotten grades good enough to get to medical school.