Walls should be more helpful as a defensive feature, currently they only serve to limit movement. Wall garrisoning is the primary defensive benefit of walls, but only allowing 8 to garrison in a long wall section means these 8 units are quickly dealt with, especially since they are stationary. Doubling the wall garrison not only looks cooler, but also allows a more sizable army to occupy walls. It should be noted that this involved adding a new row of units, not cramming more side by side.
For most civs, they look great, with ample space between the two rows. However, things are a little bit more cramped for ptol and britons, but I took measures to optimize these such that there is no clipping through the wall.
This is one embellishment for walls, with the others including decreased build time (also for palisades), decreased wall turret cost, and a +5 range bonus for turreted soldiers.