Matt Zoller Seitz in the Vulture says John Oliver Is Outdoing The Daily Show. "Last Week is doing what media watchdogs (including the Peabody Awards) keep saying that The Daily Show does — practicing real journalism in comedy form — but it's doing it better, and in a simpler, yet more ambitious, ultimately more useful way. If Stewart's show is doing what might be called a reported feature, augmenting opinions with facts, Oliver's show is doing something closer to pure reporting, or what the era of web journalism calls an "explainer," often without a hook, or the barest wisp of a hook."
I agree though I think he failed to mention the main reason. The fact that his show is weekly, not daily, means he has more time to investigate an issue. Like actual journalism. It's the thing that Jon Stewart complains about cable news networks, they're on for 24 hours a day and they don't have time to cover anything in depth. Stewart has to crank out a half hour a day (well kind of since it's only on four days a week) and basically covers the days events. Oliver can pick something important that being lost to constant harping on the Ebola scare of the day or celebrity/athlete/politician embarrassment of the moment. So he can dive into net neutrality, drone strike rules, the death penalty, Iraqi translators, and we can all learn something while laughing. Stewart could do it too but does so only rarely (e.g., with vet benefits) and cable news channels could, but that would take money away from new holographic systems or something.
The PBS News Hour manages to take deep dives often and Bill Moyers can have a calm 20+ minute conversation with someone with something interesting to say, but I can't say I've found much else on TV that manages to do so.