I think his videos are pretty damn good actually. He does a good job of picking out smart game design and elaborating on them with concrete examples, and then talks about any drawbacks that the design might have. There are some videos of his I don't care for as much, like his video on morality or the Good Horror Movie one.
The former was meh because I feel like forcing morality-based decisions on a player can limit the players options and game mechanics. Usually in those scenarios you have to choose between a bad option, and a slightly less-bad option, with no possibility for the player to attempt something else. In those scenarios, the player will eventually discover the optimal solution, and then the game just becomes "How hard can I cheese this game?"
The latter, the horror movie one (I forget the name), wasn't really about gameplay so I didn't care for it. It was just another look at how devs can do different things with storytelling on vidya than other mediums.
If anyone has other suggestions for other channels like GMT I'd be glad to hear them. As far as I'm concerned GMT is one of the few good sources on game design.