I've seen Game Maker too and i liked. Can i make serious game with that kind of tools (Game Maker, RPG Maker, Unity...)?
I don't want an "automatic" tool type. I have good programming skills with Java (OO programming) and I like to write code. What languaje Game Maker uses?
If you like coding in Java and don't want "automatic" tools, I recommend you create your own engine using opengl (for Java lwjgl). It may seem like it's very complicated, but once you start to understand the basics, it'll work much nicer (Since you've made everything, it's much easier to work with).
The only part that'll be somewhat hard will be learning opengl, but after you've written that, you'll mostly have to focus on gameplay, which will be much easier using a language you're used to.
You could also use a library like slick2d or libgdx, which will handle opengl for you.