I've been Playing and GMing since 1978 so I've seen my fair share of the Good, the Bad, and the Ugly Gamesmastering. It's interesting to see how games go down, and its very instructive to consider what works and what doesn't work with this complicated craft. I think I'll take a few moments to outline a few of my thoughts on the topic, just for the heck of it.
The Good GMs that I've played with have a number of things going for them:
- Fascinating Worlds
- Command of their Rules
- Fast Math Skills
- Natural Improvisational Acting Ability
- Passion for the Game
- Zest for Adventure (in and out of the game)
- Some inkling of what players mean by "Hero"
- A sense of Story
- The ability to Play Wicked on behalf of Evil NPCs
- At least a basic understanding of Combat Tactics
- Graciousness when confronting disagreement
- Sturdiness when confronting disagreeableness
- Descriptive Narration Skills
- Organizational Skills
- Tons of Imagination
That's a lot. And all of them help to make for the Good GM.
- Poor on all of the above
- Egotistical Behavior
- Excessive Competition with the Players (I Win! You Lose! Ha ha! mentality)
- Dumb, Silly, or Disgusting Back Stories
- Excessive Fawning over Players (neediness)
- Oh hell, all the human foibles, actually
I've pretty much seen it all. Now when GMs are Good, RPGing can be one of the most engrossing and awesome entertainment experiences in the world. You can completely lose yourself in a Great World. I've done that. Conversely, mediocre and Bad GMs can drain the life right out of you and make you want to fall asleep for a thousand years. And well, the Ugly? We don't even want to go there.
So my advice to GMs is study those points under the Good section above, memorize them, and try your best to work on getting good at those skills. There's a lot of room out there for Excellence in Gamesmastering, and only one person can turn you into one of the Good GMs. You.
That said, I don't think you could easily come up with a definitive answer to the question of what makes a Good GM under all circumstances, actually. Not one that everyone would agree on, anyway. This is because for the story aspect of the game at least it seems very much to depend much on what the group is in the mood for. Some groups want comedy. Some want horror. Some want random adventure and some want epic story. So to some degree "Good" GMing depends on the subjective preferences of the Players and what they are looking for from a game at any particular time. And players preferences are also subject to change depending on their moods. So a Good GM also has to have enough horse sense to look at the group of Players at hand and determine what they're in the mood for, and then play to that. Or, conversely, draw them into the genre s/he's the mood for and carry that forward into the game. I've seen both done well.
Ok, so all that in mind - Play On!