I've never been to Flagstaff but am eyeing a job there. Any thoughts on pros/cons/similarities with respect to Boulder?

I've only lived in Denver so far, so my views on Flagstaff are just those of an occasional tourist. So take this as a warning.

While Boulder and Flagstaff may be somewhat comparable in size (90K vs 60K), Boulder's proximity to Denver makes it easier to access a larger variety of culture, shopping.. you have more airport connections, and so on.

In Flagstaff, you are a bit more "isolated". Phoenix is almost 150 mls south. So if you do not need a big city nearby, you will probably like Flagstaff's beautiful historic downtown district, and its setting in a beautiful landscape.

Both towns are college towns, so the overall atmosphere can probably be described as "young".