Warning: Full spoilers for the episode follow...
"The Pony," named after both young Emily's present and Billie's middling career as an almost-star, got dragged down a bit by its Margaret/Owen scenes and Nucky's extremely stuffy dealings with James Cromwell's Andrew Mellon. Although, it does come as a bit of a relief to watch Cromwell give a fine and mannered performance after watching him play Dr. Nutcase the past few weeks over on American Horror Story. Those drawbacks aside, this episode helped launch Nucky forward into his inevitable, haunting "I have everything, and yet nothing" loneliness.
The pacing of this episode was amazing. Truly great show and episode today.