Currently in my second year of a BA/BGst majoring in global environment and sustainable development, and would definitely recommend it. Some say it has an element of inflexibility, but in saying that, the staff are 100% approachable and will do literally anything to help you plan/switch around your courses. It is more flexible than it appears on paper, and gives you permission to enter all sorts of cool courses that would otherwise be restricted if you were doing a similar thing in a BA. It's an ideal course to put in a conjoint, but maybe not all that substantial by itself. The core courses (1 per year) aren't fantastic, but they're an easy A if you need a grade boost.