I watched this on and off as a kid...I was too young to catch it in first run, but then it aired in reruns for a long time but trying to find it could be tricky as sometimes it was in a morning cartoon block, sometimes on Saturday mornings, and sometimes not at all. Later, as an adult, I told friends about this show and they didn't believe me...but now there's proof as it's on DVD!
Tom, Huck, and Becky are chased by Injun Joe into a cave that suddenly turns into animated backgrounds. They flee Joe through the cave (I guess it's meant to be a sort of inter-dimensional portal...) and they end up wandering through different locations and time periods, always encountering adventures with villains who look and talk just like Injun Joe.
The unique thing was that the three heroes were live-action actors against an animated background and interacting with animated characters. And for its time, it was very well-done. The animated portions were very much standard Hanna-Barbera of the late 60s.
The stories ranged from the comical to the adventurous to the downright sinister. Settings ranged from ancient Greece to Spain (where they meet Don Quixote) to China to India to a Gothic swamp to a generic medieval Europe to a valley inhabited by cave men. (No explanation is given as to why they shift time periods and location so easily; as I kid I wanted to know!) Injun Joe always showed up, as a robber captain or a Nemoesque mad scientist or a wicked king or even an evil sorcerer. (He never recognized the kids, but he was always their enemy. Again, no explanation.) Sometimes they riffed on classic literature; plots are cribbed from Don Quixote, Moby Dick, Greek mythology, and others. One episode, "The Ancient Valley," is a clear, wry commentary on the arms race, and another, "The Conquistador's Curse," is a commentary on greed with Injun Joe barely appearing at all.
In its time it was popular with kids and teens, and the young stars had their 15 minutes of fame, but actual ratings were so-so and a second season never produced.
Watching it today, it's still fun, making me remember snowy Saturday mornings watching this and dreaming of the sort of flamboyant, pulpy adventure it depicted. To modern eyes, it's sometimes primitive but still impressive, and on occasion the depiction of minorities is less than enlightened by modern standards, but nearly every group is depicted as having its good and bad, so there's that much, at least.
So, maybe not dazzling, but good if you're nostalgic like I am. I'm so happy it's now available on DVD!