The engine is a monster. Very powerful and efficient. Take a look at the airframe; notice that there is almost no room for gas. That big engine, while efficient as it gets, still sucks gas like all big turbofans, which is considerable.
What you have here is the Harrier fiasco all over again. Some jokers in the Pentagon fall in love with STOL, regardless of the fact that there is no tactical advantage to be gained. It just has a "cool factor", which does not hold up under combat conditions. The survivability rate for the Harrier (and I believe is also true of the JSF) is terrible, to the point where one could argue that you could bring down a Harrier with a well placed rock.
JSF is a nice air-show airplane. When you hang heavy ordinance on it and fill a couple of wing tanks, it becomes a single-engine slug, looking for a mission.
50% and one of my mentors is a 50%er.