What language do you have the most experience with?
Java can definitely do what you want it to. Anything that's compiled to byte-code is bound to be a little slower than something compiled directly to machine code, but tones of games are coded in Java, Minecraft and Runescape being two bigger examples which come to mind.
I'm not looking for much. Just that I want it to be able to create a decently good 2D game that can run fine on any recent machine without requesting lots of CPU or RAM.
A good enough language? I will tell you that it certainly can be done. I don't know if it'll be the best for you, it depends on your style, and what is most important to you. One of the majorly attractive features of Java is that it's a write once, run anywhere language. It's also got a garbage collector, manages memory for you, and overall, is really quite a solid language. What are you looking for in a language exactly?