Boomfiled is niice, if you want suburbia. (not the sort of place I want to be) Over all, It's the sort of place where they'll give you a hard time if you don't keep your lawn resonable or if you have a torn up Jeep in your driveway. There seems to be two parts really. The 'older' areas that were built in the 80's and the new developments where they give the houses tiny yards.
The older areas, most of the folks have lived there a good while and a good number of them in the area I lived in had modded cars or Jeeps or Motorcycles, but I was still encouraged to work on my Jeep in the garage and -not- start it up after 9 pm with no exhaust on it.
Thornton looks to be largly the same sort of area, except that Broomfiled is also it's own county. It seems like a small thing but the DMV was never busy and the people nice. It's also worth noting that in the long run, Broomfield will have higher property values because the city/county board intends to keep 40% of the land area as open space.