Forget the lousy microphones and the dinky interstitial stock music — the thing that derails most podcasts is the blab. There are two kinds, more or less. The first is that soft, inquisitive staccato popularized by Ira Glass on “This American Life,” the source from which so much pod-voice appears to have sprung.
The ubiquitous NPR Voice/Sound is really what turns me off from podcasts/audiobooks/etc. While I love NPR, their sound is absolutely grating to listen to. Too HD, rife with extremely loud and detailed plosives and sibilants. I don't want to listen to the speaker suck the spit back down their throats in excruciating detail after every sentence.
NPR's sound quality is too detailed. It's like if you watched a video of someone talking and could see the aftermath of a popped zit smack in the middle of your screen.