Greenfoot is java - you can try getting it to run through eclipse, or you can just go for straight java. I would recommend C, or C with a bit of C++ features. Microsoft Visual Studio 2015 is free and open source. Go for that. There is a guy who is coding a game from the ground up see handmadehero he put a link to his intro to C there. If you do not like Toy like languages then you will have to jump out of the high level languages and go for C, or Assembly, or if you really want to get there inside of the processor itself and learn micro code; the machine code that runs inside of the processor... I had similar feeling about Python, until I found out they had one of if not the best module for dealing with matrices, being really good a huge number computation , and being good for AI.

I, first off, see that you have not uploaded any scenarios onto the site. There is no way to determine what level of knowledge you have obtained in programming. Next, you direct your gripe at greenfoot as a language. Greenfoot is not a language. Java is a language and it is the language that is used within Greenfoot. The classes provided by greenfoot, as well as those you write yourself, are written in the java programming language. You do not have to use those classes in your projects even if you use greenfoot to write them in. I cannot tell you what should be next for you. However, I can say with a great amount of certainty that there is lack of understanding somewhere which makes you feel that way. Maybe I should point you to the java tutorials. There is an abundance of information that can be taken from them and maybe your understanding of the language will get to a point where you will realize that it is not something that should be mocked (it has not made it as far as it has for no good reason).