Seriously it was brilliant. The special effects were perfect, the machines used in it were awesome looking, the music and sfx sound beautiful, what more do you want from a kids show?
Loads of kids shows I see today are like "lol we have cuwl animatiohn, buy all our stuff plz kthnksbai." Thunderbirds, despite the fact it was made around 50 years ago, is still better than half of today's shows, and genuinely looks like it had more effort put into it than them. How's that for progress?
To justify this point, here's the first ever episode from Thunderbirds, "Trapped in the Sky". Compare it with the stuff that's on TV today, and ask yourself "Which one would I rather watch?"
PART ONEPART TWOPART THREEPART FOURPART FIVEPART SIX