We're from California and moved to Colorado back in 2000. We lived in Greeley and I worked in Loveland. Also, spent quite a bit of time in Fort Collins.
Greeley smells to high heaven. It's awful. Fort Collins, as others have mentioned, has a cute downtown area and there are some great restaurants. I found Loveland a bit depressing. Not much there and for some reason it just made me feel sad. Kind of strange.
Anyway, the other thing worth mentioning is that some people have trouble adjusting to the altitude in Colorado. We had lots of problems. My daughter had terrible migraine headaches (almost daily) and my husband and I never felt well. We lasted a year and moved back to California.
Another thing that I didn't like is the really dry air.It makes your skin itch and the inside of your nose feel uncomfortable. It may sound like a small thing, but it can be hard to get used to.
In California we were used to rolling hills and it was too flat in the Greeley/Loveland/Fort Collins area for my taste. There was a kind of desolate feeling that I didn't like.
What we liked about Colorado were the people. Pretty down to earth, nice and not overly concerned with appearances.
I worked with quite a few people who had moved to Colorado from California and loved it. So, I think our experience is not typical, but I have heard of others who had trouble with the altitude and had to leave.