I thought that at least the first two radio dramas were great, particularly the first one (which I own), which had LOTS of "deleted scenes" and expanded the overall story. I don't even think that the *beginning* of ANH started until the third episode of the RD. Another plus for the first two, Mark Hamill, Anthony Daniels, and Billy Dee Williams all reprised their original roles, which made them particularly special. The third one was IMHO awful, mostly because it seemed rushed, had strange casting (Arye Gross as Lando??? WTF???

), and didn't add anything extra to the story like the first two.
I also have the Radio Drama that they did for Dark Empire I (1995), which was pretty good as well. It's based on a series of graphic novels by Tom Vietch. The storyline focuses on Emperor Palpatine being reborn into clone bodies and his new weapons threatening the Alliance/New Republic immediately after Thrawn's demise. None of the original voice performers except for Anthony Daniels (he's just about in anything Star Wars-related) and Billy Dee Williams were present for the effort but the guest cast members sounded close enough to the original actors/actresses. If you're into the Star Wars radio dramas, I definitely suggest checking it out. There is a Dark Empire II that is also available but I haven't listened to it yet but it's not looked at very favorably, at least according to most of the reviews on Amazon.com. There is a third part, Empire's End, that makes it another series trilogy but it is no longer available AFAIK. I've seen that that they have some radio dramas available focusing on the original Jedi/Sith conflict 1000 years before ANH but I haven't listened to those either but they should probably be good.
I'd be interested in some radio dramas for the PT but it's somewhat unclear whether that might ever actually happen since the PT is nowhere near as popular as the OT was. But, of course, if there's some more money to squeeze out of the Star Wars franchise, Lucas will definitely find a way to do it. ;-)
What I'd REALLY like to see is another animated series like TCW that features the adventures and exploits of the OT characters in between ANH & ESB, and/or post-ROTJ and wish that they had done either one instead of returning to the PT era. *sigh* Oh well.