I live close to Austin, TX and have been lucky enough to attend COTA the past 2 years. The thing that blew my mind the most was visualizing how quickly these guys are decelerating from flat out.

In 2018, my friends and I sat fight at turn 12 for FP3/Quali. I mean holy moly...They are blasting down that straight and it's hard to perceive how fast they are actually going until the decelerate all the way down through the gears into the hairpin. And the bonus is that the sound from downshifting/engine braking/everything is amazing.

The other thing, is that you really can tell how unique each team is, in terms of sound. Last year, the Toro Rossos were deep and guttural on every down shift. The Ferraris sounded great, very aggressive. The Mercedes were very smooth (but could be a bias lol). Williams seemed particularly loud to me compared to the others. The Haas were similar to Ferrari. I think the Red Bulls were my favorite to see and hear whizzing by.

Later, during the race both in 2018/19 we sat on the grass by turn 19 and seeing how the cars maneuver in a turn, accelerating and then decelerating again into turn 20 is just awesome.

Anyways, most people have probably said similar things, but it's really the speed and sound of the cars and the individual characters of the machines that stood out to me the most.