While I can clearly say that we haven't been altogether successful (as evidenced by the fact that our podcast never gets referenced in these sorts of threads), I feel that our podcast (No Free Time Radio, formerly Nintendo Free Radio) succeeds where it does because all 3 of us are not playing a character. We're just 3 guys going through life who like to play games, and the feedback we have gotten responded positively to that. I feel that people come to long-form podcasts for honesty and sincerity, while brief Youtube videos specialize in someone playing a character.
Over the years we've done that show, I've found it best to keep tangents on a leash. Yeah, if they lead to interesting discussion, let them run their course but don't let it lead to rambling. Be ready to pull back to the main topic when it's clear that anything interesting to be said has. The people who are listening to your podcast come there because they want to hear what you normally talk about, so keep it on point where possible.
When possible, avoid the problem of one guy talking exclusively about a subject. It's an issue we've hit frequently in the past, and it never ends well. You have to try to get the other people in your podcast involved to keep the conversation moving, even if they're completely ad-libbing the whole thing.
The tendency for them going on hour-long tangents is precisely why I stopped listening to the Giant Bombcast, despite it being one of my favorite podcasts. I tune in to hear games discussion, not to hear you ramble on for a half hour about last night's wrestling match or your favorite bar. If you want to talk about that, create a new show around that or create a regular block of content around that rather than leave it to me to skip ahead randomly looking for whenever you shut up and get on point.
Some of my other favorites would be the classics 1Up Yours & its various incarnations and Active Time Babble & its various incarnations. Jeff Canatta's gaming podcast, DLC, is quite good as well, though I haven't listened to it in ages.