I tried Dirk Gently's Holistic Detective Agency, and never really managed to get to the end. I was somewhat disappointed cause I had my expectations up to the Hitchhiker's guide. On the subject of the Hitchhiker's guide, I liked "And Another Thing..." the most(though it was largely written by Eoin Colfer.
You may enjoy the audiobook versions of the Dirk Gently series, which are fully scripted and voice acted like a radio play. It was a really fun experience, and very well acted!