For a moment I was convinced that Davies had written one of the best Dr Who stories ever. He was riding high and everything seemed perfect until he completely ruined it by pulling out the plot hammer and everything went downhill from there.
Dr Who is basically a kid's show. So RTD wrote a happy ending and there is nothing wrong with that, except that it is the most superfluous ending I have seen in a long time. If this is writing for kids, he must really hate them or think that kids are complete idiots that must be sheltered from all the bad nasty things in the world and grow up believing that every little detail will be resolved in a happy world of ice cream and unicorns.
RTD is a master at using plotlines, he just doesn't understand the first thing about pacing or writing a truly interesting and rewarding story. All he is interested in is showing off how clever he is.
You will know where to skip right to the end, because the last third of the episode is pretentious crap that cheapens everything else that was genuinely brilliant about this episode ...