It's legal to buy them, but you can't manufacture/sell them like you used to.
For small cars (compacts, sedans, coupes), the one thing I've noticed is that they seem to have much less window space than they used to. The reason for this, I've been told, is that there's a minimum height which the top of the door frame now has to reach. In older small cars, I remember being able to comfortably sit with my arm resting on the window sill. Modern cars, my arm has to be at an uncomfortable angle to even attempt to do so. Last time I was car shopping, I had a couple people mention that it was because of a safety regulation.
Which is fine, passenger safety is a nice thing, but there then is the unintended consequence of less overall visibility when driving.
My parents had a Saturn SL2 when I was a child. The car had amazing visibility, huge windows. It felt like driving in a bubble. When I compare that to newer cars, the visibility is much lower because of the smaller windows, maybe larger vertical support beams between the front and back seats... I assume that why they started having to include back-up cameras. You just can't see as much in a modern car as you could in an older one.