In the book, Trillian was supposed to be a brunette. They only used a blond in the 1981 BBC version because apparently she was the only actress they found who "got" the script.
I actually thought the film Trillian fit this role very well.

The film characteriztion of Zaphod was utterly annoying. In the other versions he may have been supremely egotistical, but he wasn't a complete idiot too, though I think the film makers were trying to make a comment on a certain recent election and so-called leader, though they pushed the joke too far and too long. And it's a shame because the actor who portrayed Zaphod is usually quite good and the role should have been a lot of fun to play and watch. Instead I just ended up agreeing with the guy who lost the election to Zaphod and wished he had removed both of ZB's heads.

I find it odd that you did not care for the Voice of the Book, for it was the same person who did it in the other versions, Simon Jones. But somehow it just didn't come across as well with the earlier versions.

And I wish they had used the original voice of Marvin. Even though they explained why he was so depressed, somehow that got lost and he just came across as annoying, though Marvin's interaction with the Vogon soldiers near the end was one of the funnier parts of the film.

I thought the Vogons were very well done and I am glad they did not use CGI for their creation for a change. The jokes on bureacracy were good, but like many other aspects of the film, overstayed their welcome. I agree with you that the poetry bit didn't come off as it should have.

I honestly think that HHGTTG is funniest when left to the imagination - I think that is one reason the film didn't quite work, despite the fact that they followed the earlier incarnations quite well overall. Or maybe because the series was a bit more unique circa 1979. The audience I saw it with tried really hard to like the film, but I could tell it was an effort. You definitely got the feeling that the film didn't know what to do with itself halfway through.

At least one good thing came out of it: My older son, age 9, decided to think about what the Ultimate Answer to Life, the Universe, and Everything is. He came up with "atoms", as they are the ultimate building blocks. Good enough for now. At least HHGTTG will make folks actually think, which is more than I can say for Star Wars 3 or most other recent SF films.