I've listened to books on cassette, cd, and now, the mp3 version. Looks like that's going to be the format until they start beaming it into our heads. But there's been some great ones, and some not so great. I've heard narrators that either do bad Shakespearean Actor levels of narration, or those that sleepwalk through it. There's a happy medium, and the example I always bring up is Tony Goldwyn narrating Devil in the White City.
The biggest complaint I hear about the book itself is that the architecture portions are pretty dry. Well...it's architecture. But Goldwyn manages to make it sound interesting--and the rest of the book is elevated because of it.
One of my other favorites is more of a radio play, it's a dramatization of Stephen King's The Mist. The performance is from the early 80's, I believe, but the sound is pretty good on it. The actors are mostly great on it too. The REALLY neat portion is the sound. They were using some sort of 3D sound, so this is a must to listen to on the headphones. It's a trip.
In other news, just finished a huge book this week, finishing up another by the end of the week (hopefully), and then crossing into the threshold of 400 page books. Wish me luck.