Yes, it is nostalgic. Yes, it is slow, but canal boats can only cruise at 4 m.p.h. so perhaps it matches the storyline. Anyway, who says film has to be frenetic all the time? Harry H. Corbett is superb. It's a shame he never received more recognition for his talents during his life time. The film also was an early chance for Ronnie Barker to shine as Hemel's dim witted cousin. But my favourite supporting players are Eric Sykes' canal enthusiast energetically freewheeling through his scenes. He turns what are little more than vignettes into perfect sketches. Jo Rowbottom appears as one of Hemel's squeezes. Her brief appearance is actually quite touching- Hemel treats her badly, and she knows it.
If nothing else, Give it a try if you are a film buff! It's a 'spot the British character actor' film. Perfect rainy afternoon fare, except it has only been shown once on television in the last ten years.