I am an A* GCSE Maths Student, and really enjoy mathematics. You hear all these horror stories of A* Maths students doing A-Level and struggling a lot with it. Now I've heard that C1 is supposedly easy anyway (which I think I confirmed when I taught myself the basics of differential & integral calculus to see whether I'd enjoy Maths A-Level), but the other content and the content in further maths don't look exceptionally challenging.
Now I'm not trying to be arrogant, but get an understanding for what it is people find so challenging. My guess is that at GCSE you just learn facts and how to do things, but at A-Level you're required to have a deep understanding, and perhaps this abstract thinking that people aren't used to is what they find challenging? Am I completely wrong or is my guess along the right lines?