Crucially, time travel is now a reality within the show for Desmond and Daniel, with the former's visions now categorically explained. Prior to the revelation at Oxford University, Desmond's jarring experiences were well captured and gave the viewer a sense of disorientation along with the protagonist. One was forced to momentarily ponder whether the whole events of Lost were actually happening in Desmond's mind back in 1996.
Fortunately this wasn't the case and some good, old-fashioned scientific explanation saved the day. Nonetheless, more tantalising questions were thrown up, with Charles Widmore's keen interest in the Black Rock ship (seen in the first season on the island) making one contemplate his level of involvement in the grand scheme of things.
Neatly counterbalancing the scientific aspect of the episode was the prevalence of emotion, with the heartache of Desmond and Penny giving way to jubilation because of that one phone call on Christmas Eve. It was like something from a Richard Curtis rom-com, but in a good way. With added time travel and dead rats.
R.I.P. Eloise - it was emotional.