My memory is fuzzy since the last time I rewatched the first two doctors in the original series was some years ago (never did like the first two. The third was kind of ok though) but I'm pretty sure they did indeed successfully take the story from the actual TV show itself and convert it into a really crappy movie.
At least the previous movie was, as far as I know, actually an original story? Or at least it did better with what it had if not!
I don't even think this one was meant to be original. I think they really meant to just rehash the story from the series, but with a different Doctor and in color but crappier effects (somehow!)