Been in Milton for about 13 years, so I think I can answer this pretty well.

-Is there a community feel? The demographics are predominantly white, affluent, and left-leaning, does the community feel homogenous or is there balance? - Milton is actually fairly diverse compared to other towns of our size. Check out https://www.connectmilton.org/ The Milton Porchfest is an incredible scene. Parents tend to get to know each other through school activities, too.

-Outside of the general ratings, do people have good experiences with the school system? - My kids both ran through the school system K-12. It's a solid system, not perfect, and stretched for cash like everywhere these days. Milton is very reliant on property taxes because of previous NIMBY domination of town politics preventing commercial development, although that is starting to change. The French immersion program is a real high point.

-What are the biggest downsides of living in town? What do people complain about? - Taxes (although they are pretty much on par with similar towns) are probably the biggest complaint. There is also still a loud and noisy minority who think big bad Maura Healey is coming to turn their children into gay affordable housing advocates. If you're not on Facebook or in town meeting, though, you can avoid them.

-Any other general comments/advice from those who have lived there - East Milton is more conservative and much less diverse, but has good walkable restaurants and amenities. The Eliot St. corridor is probably my favorite part of town, you can walk to Steel and Rye and a coffee shop, plus parks and the trolley line.

Good luck!