So here we are, a few weeks after the listen, and I'm still pondering how I feel about Spare Parts.
I will say right up front that it's an incredible audio. The actors and the crew were clearly enjoying themselves. The production values are very high. Fans of audio dramas, even ones who may like other audios more than they like Doctor Who, should check these out. They make great background for doing all kinds of things - I highly recommend them for airports and public transit, for instance.
The thing I most like about this one, oddly enough, is that the Doctor doesn't win. He decides this time he is going to try to change what would later be called a fixed point, and he blows it - and the depth of his blowing it isn't clear till the last second. In fact, there's no telling if the Doctor *ever* finds out how much he failed. It's entirely possible he goes on through the rest of his existence and doesn't clue in.
I also like the way Doctor and Nyssa are still working out their relationship post-Adric and Tegan. Despite the fact that it's been decades since the relevant events in real time, in the story it's been... weeks? Months, maybe, and they have been dancing around it? The cast brings their years of additional experience and wisdom to the scene, portraying the relationship with finesse and wistful remorse. It's quite frankly beautiful.
It's not perfect. A few weeks out the imperfections melt away, though, and the positives far outweigh the negatives. I really recommend this one. Give it a listen.