Yuma, like any place. is what you make of it. If you want to be miserable, you will; if you want to be happy, you will. That being said, here is my list of plusses and minuses to living here:
Positives:
The weather is sunny nearly every day. When it is cloudy or raining, my kids and I do something "special" since it's such a rare occasion.
Because of the weather, you don't need to spend a whole lot budgeting for clothes -- you wear the same thing pretty much year-round!
People here are for the most part pretty down to earth and friendly. You get the occasional rude person, but I'm sure there are rude people everywhere.
It's a great place for families. There are some beautiful parks with well-maintained equipment for kids. There are lots of different athletic and recreational opportunities offered here. Even a USA Swimming club team which my daughter belongs to!
If you're really bored, and the weather is nice, the mall can be fun. If that's too boring, San Diego isn't too far away.
It's mostly a low cost of living here. The housing is (was) expensive, but our insanely low homeowners insurance rates make up for that.
Negatives:
It's ridiculously hot here in the summer. For those not here that say, "Yeah, but it's a dry heat"... well, I usually want to suggest they stick their heads in their ovens and see how they like dry heat. But I tend to get crabby when it's 120 degrees outside.

Yes, a swimming pool is great, but it is THAT hot that we don't even get in the pool until after 4 or 5 p.m.
The traffic can get messy here in the winters and the restaurants tend to be more crowded then also. But the weather is so nice then, might as well barbeque in the backyard anyway!
If you don't know Spanish (like me), that can be intimidating when you first get here. I've heard it can be a hindrance to getting a job, but I don't know that firsthand as I stay home with my kiddos.
The sales tax is HIGH.
The schools are not good. (But the positive: there is a huge homeschooling community here and the state of AZ is very lax about it's homeschooling laws. They even offer a curriculum to those wanting to stay at home so that you get materials for free and teach your kids at home. Homeschooling is not everybody's thing, but it's an option.)
We've been here for 7 years now and are just now looking at moving on. We're ready to be near family again and move to a more humid climate for my husband and son's health problems. I know, go figure -- most people move to dry climates for that! But, if it weren't for that and the family factor, we wouldn't mind hanging out in Yuma a little longer.
-M