Technically I will be a 30-something for just a little while longer, so I'll answer here.
I have truly loved my 30s, as I've had control over my life in a way I never did in my teens and 20s, and as I've been able to meet goals I started working on way back then. You are able to put things in perspective in a way you can not do in your teens and 20s (typically), so every little thing doesn't seem like a colossal disaster the way it did back then. I craved stability and was able to achieve it in my 30s. Plus, physically, it is a healthy age for most people, and for most people you come into a different, healthier relationship with your body. You feel more comfortable in your skin.
I did have some rather bad timing as far as certain world events -- we had a recession when I graduated college just as we are having currently for people graduating, and that can make things a little challenging career-wise.
It's nice, too, to be old enough to really remember the computer revolution, and to have very clear memories of grandparents who remember the industrial revolution. I feel as if my age group has ties back to a pre-industrial, pre-computer age that younger people never will understand. It really is amazing all the changes the world's gone through in my lifetime.
You also start thinking of your parents as humans rather than simply parents. As a young person, it is hard to believe anyone else was ever young, and as a result, in your 30s, you can relate easier to people of a wider age range. (At least that has been true for me.)
Having children and owning a home and having a grown-up lifestyle has been immensly satisfying to me as well.
So for those of you about to hit this decade, never fear! It's a good one!