What makes a good lesson?

I was thinking today about what makes a good lesson- I don't mean OFSTED good, ticking all the boxes in that way, I was thinking more about what qualities a teacher needs in order to make the lesson a good experience for the children.
I was in a school and I observed a number of lessons, only one of which was delivered with any sort of enjoyment. Obviously I was there and that makes it more nerve wracking for all concerned; but only one teacher actually seemed to be enjoying herself and enjoying being with the children. Interestingly she was the most inexperienced of all of them. I started wondering whether it was chicken or egg- was she enjoying herself and therefore it was a good lesson or was it a good lesson because she was having such fun? Of course the elements of were the children actually learning anything are extremely important; but they were learning in some of the other classes and yet none of those lessons were as good.
Do we need to put the fun back into teaching? Is that the elusive ingredient to getting better results? Has all the joy been sucked out of teaching and in a double whammy meant the teaching is less good?
I'll have to try out the theory, having fun means a better lesson, the next time I'm in a school!