I didn't really find the 'Tertiary phase' all that great. I think one of the problems is that the original cast members are so much older now, and it comes across in their voices. Also the loss of Peter Jones as the voice of the book really took something away from it.
I prefer my read audiobook of 'Life, the Universe and Everything', even if it is abridged.
I think Marvin's design is quite convinvcing as 'your plastic pal whose fun to be with.' Of course it flies in the face of Sirius Cybernetics appalling track record that their product should actually reflect their marketing.