I remember reading a thing by Douglas Adams where he was talking about how different in plot all the versions of the story (at the time: radio play, book, computer game) were, while still being similar enough to warrant the same title. The movie fits right in that tradition, taking elements of the core stuff, and mixing it up into something with a different shape that still works pretty well. Not a great movie, but a decent enough one. (And not cheesy, which is remarkable to anyone who’s seen the BBC production.)