Depends on the student, I had a couple of roommates drop out because they felt overwelmed, but on the flipside there were definatly portions of the program that I felt bored because the pace had slowed down from what I was used to.
The two blocks that seem to trip up the most people is the PMEL and Instrument. You have one week for the PMEL and 26 or 28 days for Instrument. If you realize that you have to work for it and commit yourself to just being a student pilot for the next six months then you'll get through.
It sucks not having a life, but whats six months of hard work for a career you want?
I'm not a koolaid fan, but having seen what my fiance had to go through elsewhere just for her PSEL Instrument, I think ATP is a damn good way to get where you want to be. Just don't be one of theose people who jump staight to an airline. I've only been instructing for a month and I already have learned a bunch more.