Yes and no.
It is great to finally see one of my favourite stories finally get the big screen treatment. There are moments where the budget has clearly benefited the overall experience, with some breath-taking CGI sequences. Two particularly spring to mind: An impressive backwards zoom out from earth's surface, past the Vogon demolition charges before the planet is so hastily disposed of, and Arthur's journey onto Magrathea's staggeringly colossal factory floor, which is simply overwhelming. Both illustrate, to great satisfaction, the dramatic readjustment of scale Arthur Dent has to undergo in such a short space of time in a stark manner that is just not possible in any medium other than cinema. The on-screen format of the guide itself is an appropriate update of the format developed for the television series, and it's highly enjoyable to see such delightfully silly animations grace a giant cinema screen.
Cinema is a different experience, and that is the nub of the matter. We are dealing with a radically different medium from any of the other that Hitchhiker's has materialised in, and not only does that offer new opportunities to explore Douglas Adams' marvellous universe, it also necessitates dramatic changes. Most noticeably, and perhaps most important for a two-hour motion picture, there is more effort to form a conventional plot than is present in the original incarnations and this change is accompanied by major changes in character motivation. This is interesting, because (here analysis becomes problematic since it is impossible to know which changes were instigated by Adams and which were down to Karey Kirkpatrick), none of the characters in Adams' earlier material really had any significant motivations that would lend them to becoming interesting protagonists in a more conventional setting.
Previously, Narcissist Zaphod wanted his ego stroked by fame and fortune, Ford was content with the prospect of a decent party to go to and Arthur's only desire was a palatable cup of tea. Trillian didn't really do anything. Although they are far from unrecognisable, the introduction of tangible drives into most of the characters alters the pattern of events in the story to accommodate what begins to resemble a more conventional story structure. One of the first casualties of this is that the principle players overshadow others, who are introduced, half-heartedly expanded upon, and then almost entirely dropped in deference to the favoured few. It never goes the whole way towards a standard structure though, as half of the principle story is seemingly abandoned in favour of a concentration on the romantic subplot and an overall resolution that is at least reverent to the previous formats. The result is a mixed bag. I found Arthur much more likable and Zaphod funnier than I ever have done, but it never actually occurred to me until the film that Arthur was a bit of a whinger and Zaphod quite boring, because I was too busy paying attention to what happened to them, rather than what they happened to do.
The other major objection, which may or may not have been inevitable, given the time that must be given over to visuals in cinema, is that the filmmakers appear to try and get too much into a two-hour film. As a result, some brilliantly funny lines are missed and key explanations fudged and both are replaced by a general silliness, which appears to be a compromise between the demands of hardcore Hitchhiker's fans and those of the cinema-going public. A lot of the new material is funny, but some of it doesn't really fit with Adams' universe and sticks out like a sore thumb. Whether this is the consequence of those responsible being caught between the rock of Adam's inventiveness and the hard place of the medium they were working in is hard to say. Perhaps someone braver could have produced something more appropriate, or perhaps this is the best that there could ever be. I suppose we'll never know.
To summarise: It's very different.