I grew up in St. Louis and never really lived there as an adult but wanted to give my input as I've lived in a number of different places.
The cost of housing is very low and there are a wide range of communities in both the city and county so there should be a neighborhood to fit most everyone’s preference. Traffic is not bad (can you say traffic is “good”?) and there is a fairly extensive light rail system.
There are lots of cultural and leisure attractions, many located in the large Forest Park and many (zoo, science center, botanical “Shaw’s” garden, and most museums) are free. The zoo and symphony are considered among the best in the county. There are many good Italian restaurants with unique specialties such as toasted ravioli and (very) thin crust pizza.
Nightlife areas include Laclede’s Landing, Washington Ave, Soulard, CWE, the Loop and more “decadent” activities can be partaken in across the river in Illinois (the only reason to go to the “East Side”). There are good state parks and lake activities (Lake of the Ozarks) 2-3 hours away and you can take Amtrak to Chicago.
Civic pride is strong and centered on the Cardinals and Anheuser-Busch (although since AB sold out that might have changed). St. Louis is very Catholic and the most important thing for St. Louisans is where you went to high school – there are more private schools per capita than anywhere else (so I’ve heard) and many families have attended the same high school for several generations (whether public or private). The main sports for kids are soccer, baseball, and hockey. There wasn’t a lot of racial/ethnic diversity when I was growing up but I think this has changed some.
In short, if you’re a young (esp. Catholic) family I think it would be the ideal place. If you’re a single transplant I think it’s definitely worth a shot as it could be a good place to settle but it will probably take a while to break in.