I checked out a few of the development studios such as Unreal, Unity and Game Maker and I would like to say that Game Maker is both a good choice and not a good choice, depending on your situation.
Game Maker is of course great for 2D games. Now with that said, I also feel like you really need think to yourself I want to make a few 2D games to really dive deep into Game Maker. What I mean by this is Game Maker has it's own language, own way of doing everything. It's not bad, but as a developer myself (not professional game developer but general developer as my day job), I know that Game Maker doesn't teach you some of the programming practices other good studios would. Now like I said, if you just plan on making 2D games, this is perfectly fine, but if you want to dive deeper into 3D, I would look more so at Unity because a lot of the stuff you will learn in Game Maker will not translate to Unity, and there will be a huge re learning curve of how to do everything. So take that into consideration before you decide on a game studio.
Not hating on Game Maker but just be warned that Game Maker is it's own thing and switching from Game Maker to Unity will require a learning curve so I would pick a studio based on what games you want to not just make now, but in the future. A little bit of Unity hell now if you do want to do 3D will pay off later. Otherwise Game Maker is fine.
Hmm, I appreciate the advice, but like you, I do have a pretty extensive background in programming (~13 years of game/web/desktop/mobile programming, CS degree, full-time non-game development job), so my concern at this point isn't "what is GM going to teach me about programming?" but "what's the best choice for this particular project at this time?"
But I absolutely agree with you about GM defying conventional programming practices, and that is a huuuge reason it was a difficult choice to switch from C++/PhyreEngine to GM for this project. GM's scripting engine pretty much requires developers to write hacky and unorganized code, but all things considered, I predict the benefits will pay off for this project in development time and generally a better end product. It's going to be a harder decision when I start up my next game (either a roguelike or an RPG) though, because GM's scripting engine's lack of flexibility is going to be a much bigger issue there...