The headlights or more accordingly the curve on the top them look like the cause of the problem. Instead of looking aggressive like the pre-facelift model's. Most of the rest could have made the facelift look better than the pre-facelift, perhaps even the vents right below the headlights, but because of the new headlights the car looks more depressed than it did.
Maybe they told it about the hybrid plans and as a relic of the 60s it wasn't quite ready for it yet.
On the bright side, it isn't the worst looking Mustang by a long margin.