Good comment. I would add that our Sun is alone, while up to 85% of solar systems are at least binary. It's possible multi-star systems make life more difficult. Similarly, Earth's magnetosphere may be uncommon, since we don't see a similar one on Mars or Venus. And maybe Earth's rotation is uncommon and many planets are tidally locked.
I wonder, though, how this stacks against the sheer size of our galaxy. There are 100 - 400 billion stars in the Milky Way, including about 4 billion Sun-like stars. Plus we keep revising estimates upward when it comes to exoplanets. Recent observations seem to indicate that 33% - 90% of Sun-like stars have rocky planets at a distance where liquid water is possible.
Are features like an unusually large Moon or a protective gas giant so rare that our planet and solar system are truly unique?
We don't know how rare either actually is. For both we have just one example - us. This suggests odds of no more than one in several thousand. But it doesn't take too many filters of that order of magnitude for a few hundred billion to become a handful, and the handful to become just one.
Your point about binary star systems is interesting. Orbital dynamics have a well-known tendency to be chaotic. In a single star system, this chaos is significantly less of a problem. But in a double star systems, the odds of moving in/out of the habitable zone over time are much higher. So that's probably a filter. But not as big of one as the ones I listed.
I wonder, though, how this stacks against the sheer size of our galaxy. There are 100 - 400 billion stars in the Milky Way, including about 4 billion Sun-like stars. Plus we keep revising estimates upward when it comes to exoplanets. Recent observations seem to indicate that 33% - 90% of Sun-like stars have rocky planets at a distance where liquid water is possible.
Are features like an unusually large Moon or a protective gas giant so rare that our planet and solar system are truly unique?