Nowadays looks more like you buy a set to follow the instructions and build it to stay on the shelf while the old sets were more like build what you can and want and play with it but it might be just our age.
The modern sets are a little less blocky (more curved parts made these days?) but seem to have just as much replay value as when I was a child. Perhaps that's not true of all of them - but then I remember my brother keeping his pirate ship built on his desk for a year or so...
You can buy basic sets still, they are fairly cheap version of lego.