Everything I think about them. As you state, just the fuel pumps (that pump fuel at cryo temperatures) are hundreds if thousands of horsepower and are amazing fears of engineering on their own. Each piece of that engine is like that.
I had the immense privilege of seeing a few F1s in person recently in DC and I was not let down.
So a little less oomph than 2 out of the 5 fuel pumps on a Saturn V, just for an irrelevant comparison ;)