As a fan of the trilogy-o-five and a bunch of Douglas Adams' other work, I was quietly skeptical about how good the Guide movie was likely to be. Douglas is gone - weirdly, a loss that still affects me personally, as if he'd been a lifelong friend - but the movie channels him to fantastic effect.
The trailer was what convinced me I needed to see it, and that whatever they'd done to it, it didn't matter. And I'm really glad I did. I'd go so far as to say that this is a classic. Yep, a classic.
One of the highlights is Bill Bailey's (Manny from Black Books - you'll recognize the voice) cameo - enough said. It's a rather short-lived performance, though.
The special effects were fantastic: the whimsical-yet-solid spacecraft design; the Vogons; the jaw-dropping Magrathean sequence; the Guide animations; the Infinite Improbability drive. The plot changes from the book were understandable and for the most part interesting, but in many cases unresolved, so the best part of all... please... let there be a Restaurant movie!
Anyway, if you were worried, don't be, it's great. Douglas would have been so proud.
Update: Rory and Chris liked it too. Seriously, it's good. Go see it. I guarantee* you'll enjoy it. I think Rory nails it - what works on the printed page doesn't necessarily make a brilliant movie. For example, the two-nuclear-missile sequence was amazingly well done, was funny in the book, but on screen it was, well, pretty heartbreaking.