I've helped teach a few camps myself and have similar opinions. Alice allowed for impressive graphics but not a lot depth to the programming (at least the early version we had at the time). Building Pong level stuff from more primitive capabilities in real Java was just as rewarding and develops skills that are a lot more directly applicable elsewhere. Learning Java by making Minecraft mods was really interesting: the initial learning curve is a bit steep due to the messy working environment, but it very quickly leads to more advanced topics as the students want to enhance the behaviors of existing creatures, add new graphical effects, or do something that requires extending the protocol for communication between the client and server. If Minecraft were open-source and the codebase was cleaned up a bit, it would be an awesome teaching tool.