The transcript of the episode can be found here
http://www.tolkienradio.com/blackriders.html.
We ended the first episode with Gandalf imprisoned at Orthanc & Frodo making preparations to move to Crickhollow, & this one will take us as far as Bree.
I suppose the first thing many will notice is the introduction of an entirely new scene: Gandalf coming before Theoden & requesting a horse, & being told to take one & begone. And the second thing is the introduction of an episode from The Hunt for the Ring from Unfinished Tales. I don't know whether Brian Sibley (the adaptor) asked permission from Christopher Tolkien to use this episode beforehand, or just took the chance & included it. Either way Christopher approved its use & its in there. Whether for good or ill is a matter of personal opinion - it opens up the story certainly, & introduces the Black Riders not as mysterious figures coming out of nowhere to hunt down the Hobbits, but as a group with a definite agenda. What the scene also makes clear is that Saruman does not fear them, & goes so far as to send them off with a flea in their collective ears. What this addition also does is to add to the sense of urgency - Gandalf has just escaped Orthanc & is headed north to the Shire on Shadowfax, & the Riders are just behind.
So there is new material, but there are also some omissions - Fatty Bolger is missed out, as is Gildor - though originally Sibley included him. Unfortunately, time constraints meant that either Gildor or Farmer Maggot had to go, & Sibley felt that the incident with Maggot enhanced the drama & gave more background information to the listener, so Gildor had to go. And, of course, the major omission is the whole Old Forest/Bombadil/Barrow Downs episode - again, time constraints meant it could not be included (though Sibley came back to the episode some years later & dramatised it, once again for BBC radio).
One nice thing about this adaptation, & something that makes it feel more 'authentic', is the presence of the poems & songs. Another is the extent to which the adaptors have tried to stick as far as possible to Tolkien's original storyline. Merry & Pippin are introduced into the story as they are in the book, & the Crickhollow/Conspiracy Unmasked storyline are kept.
Also kept are Gwaihir (a nice touch which brings home that the Great Eagles of Middle-earth are not just big birds - a failing in the movie), & Gandalf's letter & most of the Bree episode. This is a much more authentic Bree, pleasant, comfortable - a haven from the night: as Tolkien intended. And, as with Nighy's Sam, I think James Grout's Butterbur is the definitive portrayal of that character.
So, did Sibley & Bakewell succeed here? Did they capture the spirit of the book - did their 'opening out' of the story to include Gandalf's escape & the Rider's arrival at Orthanc draw you in, or should they have kept to Tolkien's slow revealing of the background?