Greenfoot is actually just meant to be a stepping stone. However, you can do a lot more with it than I think the developers meant. Your games can look quite good, just look at Nightmare: Emergence, Chicken, or my favorite, RockSmash. It just depends on how much work you want to put into your game. Most of the people on here are just using Greenfoot as a learning tool. They don't intend to sell or distribute their games.