I think Vincent is amazing as Connor. When a scene calls for angst, he delivers angst, when a scene calls for him to mope, he mopes, when a scene calls for tragedy, he soliloquies with the best of them, and when a scene calls for him to be ferocious, he looks downright dangerous, despite his Julia Roberts/Tinkerbell looks. He can also be cheerful and likable when a scene calls for it.
Is there a scene anyone can point to where his performance seems off or lacking?
But the perverse self-indulgent angst fest that is S4 ruins pretty much ever character, so Vincent didn't really stand a chance.