Personal preferences aside, the problem is not the neckline, but the proportions of this costume. Viewing from the front, down the middle the distance between neckline and waistline is too small in comparison to the distance between the waistline and private area, especially when he moves. He looks much better from the back. Just notice the difference as his spins around:
Whereas in the masterpiece that is Notte Stellata these two distances are nearly equal.