I've been involved with this course for three previous semesters. But as a graduate student teaching assistant not the instructor.
I had my own students. I had near full responsibility or class time. I wrote and graded my own materials.
Even having been involved before, being the instructor is different.
I knew I was going to like it.
I knew I was comfortable with the course content.
But it's still different being the instructor versus facilitating discussion sections.
I still have my own students.
I still mostly have complete control over what happens during class time.
I still write and grade my own materials.
The best analogy I can think of is the difference between dating lots of guys and knowing you like guys and getting married.
Even knowing you like the guy you intend to marry, it's still different when you're married. Even if you get along with your groom, it doesn't mean you won't have bad days too. Even if you've been together and committed for a while, it can still be good to learn fringe wisdom of those that have gone before.
Be nice to new teachers.
Even if they (and their students!) love what they do, they're new to it.
And help count down the number of days until break.