We talking about Skypiea? I love that arc.
If we're talking about what it brought to the series, I'll try not to add what's already been said, so I'd like to add the connections to Dressrosa and that it gave us context on the possible connection to the past, the 3rd Ancient Weapon and even the possible connection to the D's (via Enel's cover story and volume 27 cover) but spiritually it had the most development - from the foreshadowing of their conditions/paths (anything in the way of enlightenment; even all of the priests name are related to Buddhism) which served as a proper introduction arc for Ki (Zoro's air slash, Mantra).
By the way, speaking of the connections on the history, have you guys read this? It gave me some new information.
Oh but I think the most overlooked (not to mention realistic) theme in Skypiea is the fact that these people - the Shandorians, Bilkans and Skypieans think they're all different and and go to war while in fact they're actually all from the Moon. I don't know, it's just sad to me.
So I can say for certain, Skypiea had a lot of things going for it. Honestly the only people nowadays who still say it doesn't add anything are casuals, those doesn't think further, those who are behind the times and readily agreed with the people in the past on the matter or those who just wanted the "plot" to move forward after all that awesome stuff before it.
@Sephi:
I never felt Zoro himself had any kind of ego. Perhaps there are fans of his that seem it, but never Zoro himself. He's not humble but not egotistical either imo
Chopper: "Zoro is more arrogant than God!" >>> Asura >>> (I'm gonna paraphrase since I don't remember completely) Zoro: "I'll take that sword!" Ryuuma: "You want to steal Shuusui?" Zoro: "To be exact, I'm taking that sword beside your corpse" Ryuuma: "I see, you are full of spirit" Brook: "Try not to provoke him too much" >>> Zoro "vs" Hyouzou >>> Zoro "vs" Monet >>> Zoro "vs" Pica
Honestly it's undisputed fact that Zoro is pretty arrogant, more so after the time skip, it's kinda the condition with the path. But that's why scenes like his sacrifice in Thriller Bark and him asking Mihawk to train him becomes more impactful.
–- Update From New Post Merge ---
@Hajro:
Maybe they are doing an Episode of Strawhats special that focuses on the timeskip.
That would be the most obvious conclusion. Honestly it's just entertaining to see people guessing on some secretive advertisement with silhouettes, it tells you a lot about people. Could it be the Straw Hats? Could it not be? Heh.