So there are some podcasts that deal specifically in technology, and let's face it, linux, the computer geek's favorite topic. And well, they aren't very good. I'm not claiming I've listened to each and every one, but there is a common pattern to them. It's enthusiasts sounding very hyper about what they're talking about, but not in an especially cool or interesting way. It's more the kind of thing you would tune out after a while.
The reason is probably that they're trying to be something they're not. At the start of the show you're likely to have some ill conceived "cool" rock music that isn't very well chosen. Then you have the host, usually two of them, ranting about whatever is the latest fad. So they bring up a few topics and then immediately launch into the kind of monologue that you would have with your friend when talking about some cool new thing. And that doesn't make very interesting "radio". Because that's what it aims to be - radio. Only there isn't anyone responsible for the quality, and so whatever the host decides is done.
Now I may say that radio isn't really that interesting to begin with. Sure enough, these shows have more interesting content. But radio (and I mean the kind of nationwide radio that holds some standard, not random local radio) has a certain quality of form, you don't rant for 10 minutes non-stop on radio, you keep a certain pace, you pause etc. It's also about the host. A radio host is usually a person people like to listen to. A podcaster can be just anyone. Let's face it, not everyone is interesting to listen to, people are different after all.
These are shows I've listened to and they all fit the above description.