If I had to pick a best compliment, it would be from Gen Con a few years back. I had a really good table of players, including a father and his son and daughter. As the game ended and I announced we were finished, the kids let out simultaneous disappointed groans. Then the father asked what table I was going to run at next, because he wanted to sign him and his kids up for that. And they did, and had just as much fun. That was a great feeling.
I don’t really look for compliments when I run a game. But I do like noticing things like players leaning in during the tense moments at the table. Or those barely articulated gasps or exclamations that the game draws out of players. It’s a good feeling as a Game Master when you get confirmation that your game is having an effect on your players. You can’t force it, it comes or it doesn’t. But when it does, it validates everything about running games.