I can't believe some people are actually critical about this new offering. You don't have to use it! It is actually a very good idea. There are a lot of great reasons why this works:
1) It sparks the imagination for people who don't know what game they want to develop.
2) It demonstrates more complicated and powerful implementations using GM:S that people might have thought about, but not known where to begin, of if GM:S could even do it.
3) It's free.
4) It's written by YoYo so if it doesn't work, just ask and they probably can help you fix it or find a solution.
5) It gives you a whole foundation of code to use that you don't have to develop yourself.
6) Even if your game ideas are different, it can show you how to implement some feature (correctly and efficiently) that you didn't know how to do before.
7) Did I mention it's free?
IMO, this can only be positive for the GMC. Although, it is not something I will use now, I am confident there will be a day when I am grateful to be able to dig into some code in YoYo Labs to help me get started or improve a game concept.