Laclede's Landing is the only part of the original riverfront that remains (betweeen the Eads and MacArthur bridges):
The district is full of bars and restaurants, most of them catering to tourists, but several residential projects (both infill and rehab) are in the works.
Other than that, only the Old Cathedral, near the south leg of the Arch, remains.
That's the difference between European cities and American cities.
But to answer the question as to whether neighborhoods in STL are still densely-packed-- of course no city is as dense as it used to be, but St. Louis does retain a great deal of density because it's so old. Here is a pic that illustrates the look of many St. Louis City neighborhoods, now imagine this pic without all the trees. Density is still very much alive and well in Saint Louis...