OP, it hugely depends on what age range you teach, and what type of school you teach in. Primary teachers have more intense days than secondary as they have much more contact time with the kids. Primary teachers also have to be jacks of all trades in a way secondary teachers don't. Secondary teachers have much more in depth planning and marking to do, though, so while we have less face-to-face time with students, we probably spend more time behind the scenes preparing for lessons and marking work.
For me, it's a great job. I teach a core subject in an independent secondary school. I really enjoy teaching my classes and have a good work-life balance. I have small classes of well behaved, sweet kids who I adore, plenty of free periods, lovely colleagues and work 8.30-4.45 every day. I very rarely take work home and will do a maximum of a couple of hours at home per week. I also get 15 weeks' holiday a year, including a full 8 weeks off in the summer. I am paid £60k for the privilege of all of this. If I were in a state school, I would be on £20k less, have enormous classes, and probably be working until 10pm every night, which is why I no longer work in state education.
The key to making teaching work is to find the right school and stay there. You also have to accept that the first few years are really bloody hard, but once you've got 5 years' experience under your belt, if you're any good, you will find it all so much easier.
All this being said, it's still only worth doing if you love it. Teaching really is a vocation, not a job. And no, there's not much flexibility, but again, that depends on the school. In my current school, the Head absolutely would allow us to go early to see a child's play or something like that. I think now with the teacher recruitment and retention crisis, some more enlightened Heads are waking up to the reality that showing a little humanity helps keep teachers in post.