It's not the most complex game, but you're given control to build your own set of universities, trying to accomplish the goals given to you. You have a limited amount of time before the Great Evil comes and you have to start over.
Each location has its pros and cons, different graduation classes can give benefits that persist through the run, and all the building is done through picking one of 3 cards themed around what they focus on(Gold for general improvement and random magic things, Mana of particular types for rooms/items focused on that school of magic).
It definitely hits that "Simple on the outside, addictive on the inside" itch. Even playing on Marathon, a School goes by fairly quickly, so you get in that "just one more" mentality.