Somehow, I refuse to believe that Sharon did fire those last, killing shots. The gun really doesn't match up, and besides, wouldn't it just be the perfect mindfuck for the Skull to get Faustus to make Sharon believe that she had killed Cap, given how soul-destroying that would be for her? Ideal, given she played a large part in his plans.
It kind of annoyed me, though, that Civil War suddenly blundered in on Bru's plans. The focus of the issues went suddenly (although it was handled well) to the Registration Act and how Steve was fighting it, immediately after the excellent arc in London, and to me, that just lost some of the focus. It might've been Bru's plan to make Bucky Captain America all along, but I would've been intrigued as to how he would've done it.
That said, it could've been as slow as some parts of his Daredevil run, so perhaps it's for the best.