You are going to get a lot of opinions here, so here's mine, for whatever it's worth.
IMHO, nursing classes aren't so much harder as they are TIME-CONSUMING. There's a lot more work involved (than in pre/co-reqs), and you really have to manage your time to get everything done that needs to be done on time.
That said, however, if you've ever taken 3 or more classes together, you have a pretty good idea of the workload. It's just a different way of thinking. You aren't memorizing facts, you are learning to be a nurse...if that makes any sense.
LOL Why do I bother replying to posts, I never make any sense.