Hope this info is not too late for you. I live in Castle Rock and have lived in lots of Denver metro area towns. Here are my opinions of several towns:
Castle Rock: Great family area, little crime, somewhat isolated from Denver, developing rapidly. Very few older homes, brand new ones are usually the ones with front porches, trees aren't very mature, nice historic downtown castle rock section. Lower priced than other areas
Littleton: Nice family area, lots of conveniences, homes built from 1970's - present, trees are mature, downtown Littleton beautiful during winter holidays - all lit up
Roxborough Village: beautiful red rock formations, nestled right against the foothills, not very many conveniences, mostly newer homes, trees not very mature, lower priced than other areas
Boulder: pricey, college town, very pretty, older homes, mature trees, great shopping
Cherry creek: same as Boulder except omit college town, unless you count DU that is pretty close.
Aurora/Parker: wide range of homes, more towards the east (the plains), wide range of tree maturity, lots of conveniences
Golden: very pretty, in the foothills, plenty of conveniences, some older homes
Highlands Ranch: mostly newer homes, family community, lots of conveniences
Good luck on your search. My husband is from Maine and has found the lack of trees (as compared to the east coast) here in Colorado the biggest adjustment. If you think you might find this to be an issue I would stay away from the newer developments and go with older homes in Denver (wash park), Cherry creek or Littleton, perhaps Golden. They are going to be more expensive though. Sorry - don't know much about towns north of Denver. Erie has some old and new homes and is pretty isolated.