I agree with this concept. I remember where there was one GM who had the personality of wet cardboard and I just couldn't pay attention to him at all during the con game. I know that if I was to show up for a home game, I doubt seriously that I would stick around. I don't remember the game that we played other than it was fantasy (I think Herosystem).
I've played a lot more than usual in the past year (I usually GM), and the top qualities of the better GMs I've played under are flexibility, improvisational ability, and NPC characterization (this last one is something I personally suck at, and need to work on).
If the GM can roll with the punches and keep the game flowing smoothly while presenting believable and engaging NPCs for me to interact with, that's a good session.
The most important thing for a DM is to make sure his players have a good time. That is more important than how old-school or new school he is, how simulationist or gamist he is, or whether he is a storyteller or wargamer.
A good DM compromises with what his players in his party (at his party?) want to do.
Knowing that he's running the game FOR you. I don't know how many DM's I've played with that missed that fact. They'd have their 300+ page campaign outline with every NPC, plot, and decision mapped out ahead of time. Then, when the players missed something, or did something out of context, they were stuck in the mud.
I have always adhered to the simple understanding that my job is to ensure the players are having fun. I can't make all the fun, but I do have to add hooks that the players are interested in, pay attention to their backstories and motivations, and ensure that in what I'm doing I bring the enthusiasm and excitment that I felt while designing the adventure.