I'm not over 21, so I can only speak to a small number of the many great options in Louisville. From what I hear there are a lot of nice places for the 21 and over crowd. Sports bars rule the area.
There are some major companies in the area. While Louisville is, on a whole, economically down there is, it appears, an upward trend.
4th st. has some nice restaurants. However, many of them are more for the 21 and over crowd. The best things to do are go out to eat and go watch a local sporting event. The service industry, outside of food, isn't bad, but not really anything to hang your hat on.
Louisville Kentucky is a large city with great opportunities for anyone to find the job that they are looking for. There are many small towns inside of one large city, with diversified areas, and very friendly people. But most of all I attend one of the best colleges in the city. There are other colleges here to explore as well.