Hit the nail on the head. Thats what i like about ME, and if you want to specialize in another branch that is similiar, all it takes is just a few different extra classes, but the cores are all mainly the same. So theres a lot of ways you can go with it. As i stated in my earlier post I want to do something in either Automotive or Aeronautical/Aerospace, which are both pretty different from each other, but carry the same core principles and laws.
There are a ton of options for MEs in the green field. Designing dams, wind turbines, new fuel cells, solar cells, etc.. the list goes on. Thats one thing that the green field needs. To truly become independent from fossil fuels you slowly have to change the entire energy infrastructure or build anew, and engineers will do that.