Intensity is depending on a person. I did well in high school and took AP classes, and I found courses challenging but doable. Even if something is intense, it's not impossible. You have to put in hours and work to do well. I study a lot and do a lot of synthesizing and memorization. I like it though because science is interesting to me and I push through. But help is there for you. My Teaching Assistants were the lifesavers for classes.
In my personal experience, you go through a lot of material in a short period of time. It's the first semester that's most difficult because of weed-out classes. As I said, seek help from professors or TA's most are pretty nice people.
Even though classes take a lot of effort, I still have time for myself to workout, clubs, events etc.