A 'shrunken TARDIS crew' story was bound to happen sooner or later, it's an obvious idea for sci-fi writers who want to do something different other than have an exciting setting. Even though it's already been done, it wouldn't surprise me if the new series revisits it, as I think it could do it well.
Thats the key to this story - it really has to be done well. Clearly the production team put a lot of effort into Planet of Giants, even dropping an episode to tighten the pace a bit (though knowing that had to be done didn't fill me with confidence before watching this the first time!). It's the original TARDIS team in their penultimate story, launching the second season instead of the planned first, they've gone through all the character development of the first season. It's the shortest story since The Edge of Destruction, a story that proved shorter doesn't mean better. So how did Planet of Giants fare?
Meh. It by no means dreadful, but considering it had a premise that should give it a headstart in the entertainment stakes, it's fairly pedestrian.
Okay, analysis time. I'll forgive the problem coming about the doors opening mid-flight (I wonder how script editor David Whitaker missed that considering he wrote The Edge of Destruction, where it was a pivotal plot point). I like the Doctor still wearing his cloak from the last adventure. Anyway, I think the scale issues aren't the problem with the shrunken aspect of the story, the design work is very good, what ruins it is very rarely do I feel the shrunken scenes and the normal size scenes are connected. Despite the same plot thread running through them, I almost feel like I'm watching a Doctor Who story intermixed with scenes from some crime drama. It was a good idea to have something low-key and contained as the threat, but although it would require a bigger budget I think I would have preferred something slightly bigger in scale, and something that continues to be a threat once the TARDIS crew are back to their normal size.
Many of the story's flaws are minor, and most involve characterisation. To my surprise, none of htem seem particularly horrified at the prospect of being an inch tall, or in seeing giant bugs. YOu could pin this down to having seen so much in their travels already, but that doesn't explain why they tend to show more fear in the face of the more ordinary dangers of the historicals (compre Susan here to in The Reign of Terror, for example). However, I'm probably one of the few who would complain about that, and I wasn't really bothered. The 'tiny' scenes in the garden, while not exactly setting the world alight with their brilliance, stay interesting throughout.
Meanwhile, in the real world, a shady businessman called Forester murders scientist Farrow who is against the development of insect killer DN6. I liked this part of the story best, in a Doctor-lite kind of way. It's setting up an enemy and a goal for the TARDISeers other than getting back to their normal size - and a primary goal, at that. How noble. Forester is determined that the DN6 project goes ahead, and this sets in motion a plot that for once takes about the correct number of episodes to be resolved.
When the action moves to the house, and splits up the TARDIS crew, we're back with the initial teams - the Doctor and Susan, and Ian and Barbara. I've noticed that the writers have been reluctant to use these pairings since The Keys of Marinus, and it's good to see them again, but I was disappointed that the opportunity wasn't taken to give Ian and Barbara a moment to reflect together how the show started as their story. Instead, they carry on with the plot so you could swap Barbara for Susan, or Ian for the Doctor, and it wouldn't make any difference. For characters that are so different, this should not be the case. I was also disappointed that Barbara first of all got herself contaminated by DN6 then didn't tell Ian about it. She must have known she would have to tell him eventually.
One of my favourite moments of the story was the tiny TARDIS crew trying to use the telephone. Hilarious and daft, just as Doctor Who should be!
The plot continues with Forester's plans slowly going wrong, even without the TARDISeers interference. Scientist Smithers realises DN6 is lethal and withdraws his support, and the phone being off the hook has got the telephone operators attention. Even though at the climax, the point where the two different 'worlds' collide, they still felt disconnected as Forester is gassed by the miniaturised Doctor. I did like how the Doctor defeats him, and the way everything worked out made sense, but despite the faster pace of the last episode, this wasn't a terrible fulfulling story. Aside from the flaws I've mentioned, Planet of Giants suffers by seeming so ordinary. It has a good premise, but aside from that, if I had to say what I liked about this story, my answer would be.... very little.
Horror quotient - Louis Marks evidently decided this wasn't a scary story, though there was a golden opportunity to make this a real classic if he had went in that direction. Perhaps they were already planning The Web Planet and opted not to push the 'giant bug' angle?
Comedy quotient - A few inevitable laughs because of the premise.
Drama quotient - Usually when there's not much horror there is more drama to make up for it, but there wasn't much of this either! It was the strongest aspect, especially in the normal size plotline.
Good, solid, reliable Who about sums it up.