When I interviewed John Oliver in the spring about the impending debut of his HBO show "Last Week Tonight with John Oliver," he admitted that they still didn't entirely have the formula locked down yet, and were experimenting with different ideas for how to structure the show.

But if Oliver and his team didn't know in late April exactly how "Last Week Tonight" would best function, they figured it out in a hurry. Within an eyeblink, the show established itself not as a weekly version of Oliver's stint as "The Daily Show" fill-in host, but as a very specific, powerful, wonderful thing. It became so beloved so quickly that they could spend a good chunk of last night's first season finale with a segment whose primary purpose was to show how many famous people and TV shows wanted to be associated with what Oliver was doing:

Other late night shows have done similar star-studded gags — see Colbert's "Get Lucky" dance party — but they've tended to be ones that spent years building up the kind of celebrity adoration needed to make this kind of thing work. But everyone has fallen instantly in love with "Last Week Tonight," from Tom Hanks all the way up to R2D2.

So how did Oliver and company generate such fervor, and figure out how to make "Last Week Tonight" something other than "The Weekly Show"?

1. They took advantage of the format and the channel to go deep.

The signature element of "Last Week Tonight" became a long feature — often running 13 minutes or more — in the middle of the show that would allow Oliver to explore every possible angle of humor and outrage (more on that in a minute) in a given story, from rampant corruption in FIFA, to our nation's prison system, all the way to last night's segment on state lotteries. "The Daily Show" rendered the "Weekend Update" formula on "SNL" largely obsolete by covering the same topics in much greater depth, exhausting their comic possibilities by the time Seth Meyers would get to them for one or two punchlines. "Last Week Tonight" took that even further, picking one subject for each episode and deconstructing it so thoroughly that there would be no point in anyone else bothering to approach it in a similar vein in the future. Though, with few exceptions, no one else would also bother because...

2. They covered stories no other show would.

In that Oliver interview, I asked how he might deal with the topic overlap with "The Daily Show" and "The Colbert Report." It turns out that this wasn't really a concern, because his areas of interest were different from his old pals at Comedy Central. It's not just that "Last Week Tonight" did very little satirizing of the news media, but that it explored subjects the news media (real and satiric) had little interest in covering.

"The Daily Show" and "The Colbert Report" are TV news satires that also feature jokes about subjects that are in the news. "Last Week Tonight" became entirely the latter, and picked topics that are generally under-covered by American TV news — both the real and fake kinds. As an immigrant, Oliver's unsurprisingly more interested in global news than many of his peers; the first episode dealt with the Indian election, and at various points the show went deep on the question of Scottish independence and anti-gay laws in Uganda. But he also made a segment on net neutrality into compelling TV — and helped briefly crash the FCC's website by inspiring his viewers to chime in with their own opinions on the subject — and even devoted a large chunk of his second episode ever to the death penalty, a decision even he couldn't quite believe he had made as the segment was beginning.

3. There was outrage, but also creativity.

One of the ways Oliver's "Daily Show" fill-in stint distinguished itself from the show we know under Jon Stewart was in how little Oliver bothered trying to disguise his moral indignation over the stories he covered. On both "Daily Show" and "Last Week Tonight," his default attitude has been "Can you fucking believe this?" But he pulls it off because of the unexpected ways he finds to insert humor into otherwise angering and/or depressing topics. The prison segment concludes with a musical number featuring Oliver and a group of "Sesame Street"-style puppets. He talked viewers into sticking with him for the death penalty segment with the promise of showing them a video of a tiny hamster eating a tiny burrito. And as the latest Supreme Court session closed recently, he offered aspiring parodists everywhere the chance to recreate various Supreme Court arguments with dogs sitting in for the nine justices.

"Last Week Tonight" will be back on February 8, and I'll be curious to see what, if anything, changes going into a second season. Back in the spring, HBO boss Michael Lombardo said there had been talk about eventually expanding the show to an hour, or more than once a week. For the moment, it seems nearly perfect as is (some of the transitional running gag ideas could use a bit of polish), and HBO has very smartly leveraged social media by putting the majority of each show up on YouTube the next day, recognizing that, at least for now, the show needs to be virally available in the same way that Stewart or Colbert or Fallon clips are (and also that a show like this won't have great demand for people to revisit old episodes the way that a "Sopranos" or "Game of Thrones" would).

What does everybody else think? Did Oliver impress and/or surprise you with this inaugural season? Did you have a favorite segment? Are there any tweaks you'd like to see them make over the winter?

Alan Sepinwall has been reviewing television since the mid-'90s, first for Tony Soprano's hometown paper, The Star-Ledger, and now for HitFix. His new book, "TV (The Book)" about the 100 greatest shows of all time, is available now. He can be reached at sepinwall@hitfix.com