I lived in KC area for about 3 years right after college. In fact, I got married there. I lived on the plaza the first year and Overland Park after that.
At the time, I couldn't wait to leave. Thought it was boring and flat with nothing to do but eat and shop. Its actually true; kinda boring, it is flat and not much to do but eat and shop

. BUT, after living there, then NW Montana and now Denver metro, I really do appreciate KC. Its not perfect, but its actually a pretty good place to live, especially Johnson County (Overland Park). It is very similar to Highlands Ranch as far as the suburban feel.
denvers downtown is better than KC, but KC has the 'plaza' as its alternate. Its like 16th street mall, only much bigger. Its a few minutes from KC downtown. KC downtown, at least in the mid/late 90's was a little scary after dark.
The terrain is definately flatter and not much to do except go to the ozarks or sit in a corn field. But its also much greener with real live trees everywhere! Not the 1.5 standard builder landscape trees around here in south denver metro. Fall is really beautiful in KC. You really get a sense of Spring at springtime. It comes and goes too fast here in Denver. I really miss driving along Ward Parkway in the fall.
I'm a huge Broncos fan and was long before living in Kansas City or Denver, but I will give KC the nod as being the better football town. The atmoshere there is awesome for football/tailgating. Better fans if you ask me. That makes fall there that much better. (it wasn't fun being a Broncos fan while living there, however

)
Weather is definately better in Denver.
Johnson Co is pretty safe (or was-assume still is) but the 'bad' areas of KC are much worse than the 'bad' areas of Denver IMO.
Great BBQ culture there. Good restaurants of all types all over.
Overall you'll like it there. Just plan on taking a few vacations to get away- at least once in winter, and once in summer.