I have to admit that I am a little surprised by the reviews and rating for this movie. I actually found it quite funny at times, but I grew up with the show. I think what ultimately pulls this film past an average outing is the facts that some of the one-liners genuinely are funny, and my own personal affinity of the characters.
That's not to say that there aren't a few issues with the film. While the cast doesn't have to be regulated to the store to be funny (Grace and Favour proved that years later), they didn't have to transport the same jokes. There were at least 2-3 scenarios taken directly from the more popular episodes. On one hand, it's not the most original, however funny it was the first time, on the other hand, one has to take into account that some people may have never seen the show, and this movie is their first exposure to it (And shame on you, if so).
The biggest problem is that the plot relies too heavily on the likability of the characters, and the one-liners they shoot out. There are several inconsistencies, the ending is startlingly abrupt (yet ends on the same note as any of the episodes on the show), and plot-wise, they don't do that much. The Grace Brothers staff never gets out to explore their surroundings to add to some new situations and jokes. Again, the innuendos are funny, but the middle of the film drags in terms of things actually happening.
I don't think this film is worthy of its current "3" rating it has. It has it's moments, and the main cast shines in their personalities and silly hi-jinks (the supporting actors don't give the main cast much to work with, however). I think the biggest problem is that it's set up like an extended version of the show, minus the laugh track. You can see the television show format in it, and I think that ultimately hurts the pacing.
Perhaps this would be better for fans-only of the show, or people who haven't seen the show at all. It's not one of the best "episodes" of the series, but it's better than it's been given credit for, outside of some obvious flaws.
