I'm from Boston, and grew up listening to talk radio (i.e. conservative hosts, very much opinion-based, little prima facie unbiased reporting, &c). As I grew older, I realized I should expand my horizons and maybe try the NPR in the area, thinking that, as I was in Massachusetts ("tax"achusetts, the people's republic of Massachuetts), I would get a very different side of the radio "coin" as it were, with liberal vitriol and left-leaning moralistic rants. I daresay I was wrong. WBUR hosts the local NPR station and though the hosts tend to be left leaning, they are great at presenting both sides of many issues with striking equanimity, not to mention how incredibly interesting their guests are and polite their on-air demeanors are compared to their talk radio counterparts. The programming is great, with some in-house anchors as well as some syndicated shows throughout the day. I consider myself a libertarian and I can't even listen to talk radio anymore it has become that grating and absurd. In all, I would say a slight to moderate liberal slant.
P.S. one thing, though. While talk radio had it's bias slant as almost a banner of the station, NPR may suffer from a slightly more insidious approach to news, which is to say their content may be skewed slightly toward the liberal side, covering many green initiatives, rights-abuse scandals and the like. This, however, does not effect their reporting or discussion in any way, making them much more enjoyable and frankly more level-headed than their competitors.