If I where to create a Metroidvania game in the style of SOTN, what programming language should I use?
Python, Java, C++. etc. Anything goes. I am planning to create a sequel game to SOTN based on Castlevania Nocturne of Reminiscence.
Well, he never said "free language". Game Maker DOES do some cool things on the free editions, but indeed, he'll have to buy it so he can have access to everything the engine can do.
PERSONALLY, the money was one of the best I ever spent. Even though Game Maker Studio is still in development (with new features being added in real time to it, sometimes o.O), I was finally able to kick forth my projects and am seeing them finally gaining life.
For me, it was the easiest experience, with the quickest payoff. But, as VladCT put, C++ might also be good, since it was my second option to learning Game Maker.