For starters, let's say that this film is really....different. It is a great combination between suspense, comedy, and an oddly, romance. As a private detective, American, residing in London, Chevy Chase is hired to do a job that goes south and results in his own murder. Because his final destination is indeterminable, the powers that be send him back as a "returnable" to solve his own murder. The catch is, the only body available is a scruffy dog about to be hit by a garbage truck - enter Benji. By far, this is Benji's most adult film. This is not just a cutesy dog movie that you are used to seeing Benji in - there is definitely adult humor. Jane Seymour is beautiful and makes conversation with a dog seem totally natural (pretty remarkable if you ask me). For you Pride and Prejudice fans, look for a younger version of a famous occupant of Rosings Park.
Chevy Chase does a remarkable job conveying his character when you consider the fact that most of the time, we only hear his voice and see Benji, whose actions were, I'm sure, not entirely predictable. As little as we see him, you still know Chevy Chase is there - because his undeniable wit never lets you forget his presence. The mystery is intriguing, even though we know from the start who the murderer is. The pleasure is watching our villain become aware that he is being outwitted by a dog.
Another thing to look for - when Chevy Chase is in Heaven, watch for the special effects and sounds that are humorously borrowed from popular sci fi of the day (star trek, etc.), including a direct reference to Star Wars. On top of that, the film has a marvelous soundtrack, including songs by Paul McCartney and Elton John. Watch Jane Seymour driving her convertible along a country road to Elton John's, "Return to Paradise", and tell me it doesn't get stuck in your head.
If you appreciate Brittish humor, great actors, and some "cute, fluffy types" thrown in for good measure, then settle down on a rainy afternoon and enjoy O Heavenly Dog.