i spent a lot of time online looking for the original series i myself enjoyed as a kid and found it at last. In the process of this i purchased spin off films, which are i believe are dreadful by comparison.
The plot follows a basic story line, bunch of kids stumble across a 'ghost' with a crime involved - a mystery. They solve the mystery, by uncovering various clues while being chased around by a ghost who turns out to be a bad guy dressed up. Quite fun and still enjoyable today.
AND as there are 24 episodes, your brain wont go numb watching the same DVD over and over again with your kids.