I always felt that the first two novels, "The Hitchhiker's Guide to the Galaxy" and "The Restaurant at the End of the Universe", where far better than the last three. Almost to the point where the three last novels aren't worth re-reading.
YMMV, but I just finished laughing my way through the unabridged, author-narrated(!) "The Long Dark Tea-Time of the Soul" audiobook; for me, the experience stands up to the best of his treasured early works. The opening chapter (getting to the airport) is singular. Don't miss it! :)
After the Dirk Gently books have a go at Neil Gaiman's Good Omens, co-written with Terry Pratchet. I also highly recommended Robert Rankin's Brentford Triangle "trilogy" (in 9 books).
