I saw it at a Landmark, which is half mini-plex, half art-house. I saw trailers for The Fantastic 4, some Irish lesbian flick (!), and several forgettable descriptions.
Let me just say that I've read all but 2 of DNA's books, and those two I can't find in person;* I will laugh at any comedy, and a few bad jokes; third, I also read every bad review of the movie so I could go in with low expectations (I find it always goes best that way). I read a few good reviews, but 60% on rottentomatoes** usually means "Terrible Film." I read that folks who don't know the book(s) will enjoy the movie almost as much as those of us who do.
That's baldly false, and I've got a wife to prove it.
Now: SPOILER ALERT. It's tough to imagine a better translation to film as the source would allow. Humma Kavula was a good plot invention not only to replace both the styrofoam head which failed so mightily on TV and Zaphod's book-based Brain Surgery Inscription, but also to include the Great Green Arkleseizure. I thought Rockwell was on point as Zaphod, and Zooey Deschanel exactly fit the physical type for Trillian, though her hair should have been short, I thought. (Coincidences with Elf: the cheek-kiss was the same at the fancy-dress party and Rockefeller Center, and she was filmed showering in both films. God, no matter how much it sounds it, I didn't mean that creepy.) Mos Def was good as Ford, who was never much more than Arthur's impetus; speaking of whom, Martin Freeman was the perfect Arthur Dent.
Comparing the book(s) to the movie will always be disheartening: a Hollywood Film requires: story, tension, and either romance or resolution. The books, singularly or wholly, lack story, tension, resolution, and romance. Furthering Arthur's relationship with Trillian is something that is fated to happen in this medium. I thought they played it off well, and as a fairly minor point in the overall plot. If the H2G2 canon can be said to be about anything, it's about Arthur learning how to be himself in an area of undefined dimension. Trillian and Ford are his motivations to do so in this version... lest we forget that one dimension's Trillian bore some dimension's Arthur's baby according to a later book in the series...
Ye gods, I'm rambling. G'night!
*there's just something about going to a bookstore. more so: a library.
** I didn't read their linked reviews, but geek-and-fan reviews.