1 3 5
1. At the start the radio plays and books are close together, and are on a wild, Arthur-Dent-disorientating high, though I think I preferred reading rather than listening to some of the bits about the bad-poetry-obsessed Vogons, the nutty probability drive, the ancient computer Deep Thought and of course, the restaurant at the end of the universe (apparently Douglas was fond of a good restaurant)... but we are straying into the "secondary phase" of the series...
2. In the secondary phase, the plot revolving around the people who have evolved into bird-like creatures is rather odd, and was a low point for the radio play series for me, and which I think was cut when this became the 2nd book in the series. The Golgafrinchan civilisation outcasts (mostly telephone sanitizers and estate agents) towards the end are amusing though, and the extra bits scattered throughout from the Guide itself are, as always, wonderfully daft.
3. Hilariously riffing on xenophobia, British past-times and second chances, as well as amusingly tormenting Marvin the thoroughly depressed android with a flock of sentient mattresses (really), this third radio play series works expecially well. It's long since I read the book version Life, the Universe and Everything but apparently the plot is the same: The peaceful people from the planet of Krikkit who suddenly decided that the rest of the universe "has to go" and Arthur, Ford, Zaphod and Marvin get caught up in the trouble.
4. My memory of reading the fourth book is that it slows down a bit too much when Arthur meets Fenchurch. The radio series perhaps has done a better job here of showing their romance while keeping the gags and odd things happening, and the trip up the sacred mountain is actually touching and funny too - why do we root for this android so much?
5. There's a lot going on here, and it's all great. Ford seems more at home amongst the peril as he uncovers what has been unfolding at the Hitch-Hiker's Guide headquarter, and I particularly like another robot that is introduced - Colin - who Ford reprograms to know happiness and proceeds to be happy about - well, just about everything. The plot here is strong too as Arthur and new character Random (born more or less at random) have to get to grips with something threatening all the parallel earths. A high point for the radio series, as it streamlines the best bits of the book. I remember the fifth and last book being one of the funniest too, apart from some of the bleakness in it.